A great resource for most any question you may have regarding tickets at WDW is the Everything About WDW Tickets post on the DISboards. It is written by a Ticketing Cast Member. So why bother with what's below? Well, despite the post, plenty of people still ask lots of questions, over and over and over...
CMs have reported that they have LESS issues with the Tyvek cards than plastic, especially with regards to the magnetic stripe. Reasonable care should make them last perfectly fine. If it was a problem, Annual Passes wouldn't be issued on them.
That said, any ticket you get at WDW (unless issued on a Key To The World card) will be Tyvek.
It appears that tickets purchased and mailed to you are usually plastic. This may be due to them standing up better in the mail. I've also gotten plastic tickets from AAA, but have also heard of them issuing Tyvek tickets as well.
If you have ANY ticket issues, you should be able to get them reissued easily. Having copies of the backs of the tickets may make it faster, but at least have your ID.
Regardless of whether they are Tyvek or plastic, reasonable care should keep your tickets in condition. Keep them in a waterproof holder, and arrange them such that no magnetic stripes contact another.
Prior to 2005, days on tickets never expired. MYW tickets now expire on the 14th day after first use (including the day it is used), unless you purchase the "no expiration" (NE) option. So, if you use a ticket the first time on a Sunday, you must have used all days/options on that ticket by the end of the second Saturday. Unused MYW tickets NEVER expire.
The Park Hopper option is the same price - $55 - no matter how many park days you have on your ticket, or how many you have not used yet. The exception is a 1-day MYW ticket, where the Park Hopper option is only $35. If you upgrade a 1-day PH ticket, you'll also have to pay the additional $20 to upgrade the option.
If you are unsure if you need or will use the PH option, do not get it in advance - you can always add it when you need it (see "Upgrading Magic Your Way tickets"), as long as you do it within 14 days of first using the ticket.
A park "day" is considered to be from the time the park opens to guests until it closes to guests. Even if there is an Evening Extra Magic Hours that runs until 3am, the hours from midnight to 3am are considered part of the previous day.
If for some reason you happen to have two separate park tickets (say, one from a previous trip that was non-expiring), then you could use a day from each ticket instead - but this may not be the most cost effective use of a second ticket.
Unlike park days, each one of these pluses count as true "admissions", and you can use more than one a day. So if you went to Blizzard Beach in the morning, did a round of golf at Oak Trail, and then DisneyQuest that evening, it would cost you three pluses.
Like park days, all pluses need to be used within 14 days unless you get the No Expiration option. If you do get NE, the WPFM becomes very valuable because for the extra $55, you get a number of minor admissions that never expire, so even though you may only go to one of the water parks once a trip, you could pre-pay for up to 10 water park admissions in the future. Even if you use up all your park days, the WPFM options are still good.
Another thing to note is that if you add additional park days to a WPFM ticket, you also get the additional WPFM admissions.
The cost of the NE option depends on total number of days on the ticket (used or not), starting at $25 for 2 days, up to $225 for 10 days. This is the one option that gets more expensive as more days are added.
However, getting the NE option should not be done lightly. If you are local enough to Disney to make day trips, or at least short ones, it may make sense. But if you can't fit full vacations within the length of ticket you purchased such that you need to purchase an additional ticket, you will probably spend more money.
For example, lets say you got the maximum ticket - 10 days, no options. The adult base price is $291. To add the NE option is an additional $225, so now its $516. If you used 7 days on your first trip, you now have 3 days left. But if your next trip will require 4 park days, then you will have to purchase an additional 1-day MYW ticket for $85, so now your pre-tax total is $601.
If you had stuck to a 7-day base ticket, and then gotten another 4-day ticket on the second trip, your total cost would have been $267 + 243 = $510. You ended up spending $91 MORE to get the NE option...
If you already have a NE ticket with leftover days, and an upcoming trip requires more days, you are better off keeping the NE ticket for a future trip that you can fit on it, and purchase a separate ticket for the one which requires more days.
You can add the PH, WPFM and NE options within 14 days by simply paying the amount it would have cost as if you had gotten it in the first place - nothing is pro-rated. For the PH and WPFM options, that is $55 each. The NE option depends on the number of days on the ticket, both used an unused. So, if you have used 7 days of a 10-day ticket, you still pay for the NE option based on the 10 days, not the three left.
You can add days to a MYW ticket, so long as the total number of days on the ticket (used or not) does not exceed 10. If you need more than 10 days, you either need to purchase an additional ticket, or more probably get an Annual Pass.
Upgrades do NOT extend the expiration time or upgrade window of a ticket - it remains 14 days of first use, regardless of what upgrades you perform when. The exception is when upgrading to a non-MYW ticket that does not have the 14 day limit, like an Annual Pass. However, when upgrading to tickets that expire based on a particular date, the date of expiration is based on the first use of the original ticket, not the upgrade date. For example, if you have a 7-day MYW ticket you first use on May 1st, and add the PH option on May 5th, the ticket still expires on May 14th. If you then upgrade to an Annual Pass on May 11th, the expiration of the AP is May 1st of the next year.
Here is a tip: If there is any chance the ticket you have was discounted from the "gate" price (the price you'd pay if you were purchasing right at the park) or purchased before a price increase, use it at least once first, and THEN upgrade it. A used MYW ticket should (and I say should - some CMs do not always do this properly) be credited at the full gate price, not the purchase price, when applied to a new ticket. This is referred to as "price bridging".
If the ticket fails to read in the turnstile or it is old enough to not have a magnetic stripe, you can get it re-issued at any ticket booth or Guest Relations.
APs also include free parking at the theme parks, so if you are staying somewhere other than a Disney Resort, this could factor in to your decision to purchase as well. And that is just among the various other perks that an AP holder can get, such as room discounts, dining discounts, and more.
The adult standard AP price is $519. A 10-day NE PH ticket is $571 - so if you are going for 10 days in two separate trips in a single calendar year, the AP is definitely the way to go, and that didn't even factor in other potential savings.
You can also access the WDW Passholder web site even before the pass is activated to see all your benefits, and even make plans based on discounts. You can always book AP discounted rooms, even though you do not yet have an active Annual Pass, but if you do not show a valid AP to the resort staff by about 24 hours after check-in, you may lose the discount.
The DVC Annual Pass is otherwise the same as their counterparts.
A DVC Member can only purchase APs at this price for themselves and members of their immediate family who reside in the same household. All adults must be present at time of purchase/activation, and must have valid personal ID with their address matching that of the DVC member.
Note that the DVC prices are not considered a discount, but a specific ticket price, so if other discounts are available, they can usually be used in conjunction with the DVC price.
You must always use the same finger. It should be the index finger on your right hand (the side the scanner is on), but if for some reason you did not use that one, make sure you always use the same one. Some CMs might try to "correct" you to use your index finger even if you know which one is the right one.
Guests on child tickets (3-9 years old) do not use the finger scanner at all.
According to Disney, it is NOT a full fingerprint scanner. It is relatively low resolution, and after normalization (to account for rotation, distortion, etc.) some data points are chosen and turned into a numerical value, which is what is actually stored in the ticketing computer. The likelyhood of two people being identified with the same finger scan is on the order of 1:10000 - much more common than a true fingerprint match. The technology used is actually fairly common and and what Disney says is pretty much correct. Full fingerprint scanning would be difficult and slow.
Sometimes, and under what circumstances is unclear, tickets that are purchased together may be linked together in the ticketing computer such that a finger scan for one ticket might be accepted for another. This can help prevent "turnstile confusion" wondering whose ticket is whose - but this cannot be relied on, so it is highly recommended that you somehow identify which ticket belongs to which person in your group.
Also, at times the scanners may actually be turned off to help the flow of people, and you may not be required to scan your finger.
In addition, if they obtained an Annual Pass or Non-Expiring ticket or other similar long-term ticket that was used before turning 10, you can upgrade that ticket to an Adult ticket at no extra charge. The child needs to be present during the upgrade, and the age difference needs to be reasonable - if the ticket was obtained within the past year, but the child is obviously 16, then it can be denied.
If the ticket is unused, however, you can only receive purchase credit towards the price of an adult ticket.