I think the common gotchas:
Points at DVC don't change - points for other options - like cruising or staying at the Disney hotels or staying at the Broadmoor - can change from year to year and usually go UP. You need to understand where the value in your purchase is....
Likewise, you need to understand how you travel and if this will change the way you travel. Often people PLAN to save money using DVC - and you can. But, many DVCers discover that this changes how they travel. They might intend on studios, but stay in one or two bedrooms. They may think "one trip a year" and take two. They may think "our family of four" and invite their brother and family. They may intend to use the kitchen, and discover they don't want to take the time.
The seven month window thing - usually, if you are flexible and call right at seven months, you can - more or less - get what you want. But DVC books fairly completely year round - eventually - and sometime room types book right at eleven months. Don't believe that a standard view BWV room will be available at seven months the first two weeks in December every time you try (you might get lucky - you might even get lucky a few tiimes), or a OKW Grand Villa over Thanksgiving.
Dues - pay attention. "Around $4 a point" doesn't sound like much, but when you are getting a $1200 bill every January, the $.16 point increase may be a big deal. Dues will be where you spend the majority of your money with DVC - don't discount them up front.
Perks - current perks are pretty good. But don't buy DVC thinking they will last forever or that Disney "owes" you discounts in reward for your loyalty. Perks have been good and bad, and will likely be good and bad in the future. Plan on getting only what you are contracted for and you will probably be very happy.
Room Condition - we've always found our rooms and the DVC areas acceptable, but I think there is a noticable difference between upkeep at DVC resorts and upkeep at the Deluxe hotels. If you are expecting a Deluxe hotel experience, you need to remember you are staying in a timeshare.