I am interested in purchasing DVC membership.
as deb&bill says, first you should think more in terms of "ownership" than "membership." you would be purchasing a long-term real estate interest...a lot like a 30+ year lease. DVC represents prepaid accommodations at DVC resorts (about 7 onsite at wdw, 1 at hilton head, 1 at vero beach, 1 tiny one at DLR and 1 in hawaii.)
if things change in 10 years and you no longer want to go to wdw every year, you would still be responsible for the annual dues until you sell that real estate interest or until it expires (which varies from 2042 to 2060 depending on which resort you commit to purchasing.)
if you buy in, disney would be offering you a (relatively) fixed deal on lodging costs. but be aware that
disney would no longer be willing to offer you discounts like "free dining" or "40% off" or "7-for-the-price-of-4." if the economy improves and disney continues to raise lodging rates as they have done in the past (while cutting back on discounts), then you will come out ahead - otherwise, you may be disappointed.
DVC is only for lodging costs, so you would still be on the hook for travel costs, tickets and food.
there are currently numerous perks that are nice for members: dining/shopping discounts, about a $100 discount on an adult AP, pool hopping and free internet during stays. these can go away at any time.
you pay a certain amount upfront to buy a contract (over $100 per pt direct, usually less than $100 resale) - similar to buying a house. then you pay maintenance fees every year - to pay for insurance, utilities and upkeep - similar to owning a house.
the DVC works "best" for people who:
1) go to disney at least every other year
2) prefer to stay onsite at deluxes (or at least moderates)
3) can plan their vacations 10 or 11 months in advance
4) can limit Fri-Sat stays since weekend point costs are a little higher
5) intend to use DVC primarily for staying at a DVC resort at disney (rather than trading out for other timeshares or cruises, etc.)
6) need or prefer larger accommodations than a basic hotel room
OTOH, there are lots of good reasons to balk at buying DVC:
1) thousands of $ upfront plus annual fees require a certain level of financial ability and commitment (and you still need to pay for tickets and travel, etc.)
2) commitment to wdw/fear of wdw burnout (sorta - while you can trade out if you buy direct, the best value is staying at the DVC resorts)
3) DVC not as deluxe as deluxe hotels in some senses (limited housekeeping, sofabeds, no room service at some DVC resorts)
4) financing a depreciating (sooner or later) luxury purchase is generally a poor idea
5) happy with value hotels
6) amenities like a kitchen and washer/dryer have no value for you
7) you don't/can't plan vacations 6+ months in advance
8) you enjoy hunting for deals/bargains for each trip
If you’ll be upset when other people can pay cash for a room and get a discount or get “free” dining thrown in, then DVC is not for you.
also be aware that if you think you might keep DVC for 6-8 years and then sell it down the road, it may have little to no value as DVC has begun cutting perks that transfer when you sell your contract.
here is a link to a basic DVC FAQ.
here is another FAQ