DVC is best understood as prepaid accommodations at DVC resorts (about 7 onsite at wdw, 1 at hilton head, 1 at vero beach and 1 tiny one at DLR.)
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 - so it's best to make a decision based on the long-term real estate lease interest (expires in the year 2042, 2054, 2057 or 2060, depending on the resort that you buy an interest in) that DVC represents as opposed to paying for onsite hotels at wdw every year.
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
it's been worth it to me and a great value, but i only bought enough for onsite stays at wdw. (BTW, there's a "do you regret anything" thread on this page that you should also look through...)