A few things to look out for:
1. Make sure you are wanting to buy
DVC with your primary intent being to stay at the DVC properties. DVC does offer exchanges which let you stay at other WDW properties and even non-Disney vacation destinations. But these are not "economical" uses for your points. DVC is the Cadillac of timeshares. If you only want to go to Disney World every 3-4 years and use your points elsewhere frequently, then you're better off looking into other timeshares. You can get something cheaper which will accomplish similar goals.
2. As rocketriter suggested, look at the
point charts. Weekend stays often cost more than 2x the number of points as the same weekday stay. There are many different "seasons" with different point costs per night. Make sure you buy enought points to accomplish your vacation goals.
3. Realize that DVC members are long-term planners. Getting a room--any room--on short notice (let's say 2 months or less) will be difficult in some periods and downright impossible in others.
Other than that, there aren't a lot of pitfalls that stand out. There is no wording in the contract that allows DVC to take your first born. If you buy direct from DVC, the prices are not negotiable so there is no haggling over price.
If you are used to staying at WDW Deluxe resorts at least every 24 months (if not more frequently), there is no question that DVC will save you thousands in the years to come.
Good luck.