The key is planning early. Buy where you want to stay most often, and book at your 11 month window. I've been a member since 1992 and never had a problem booking up to 3 rooms. And although I ultimately haven't stayed at other resorts besides OKW, I have been succesful in booking them at 7 months, but my plans changed and I had to cancel.
You may have problems trying to book at the 7 month window for popular times, like Easter, Christmas and Spring Break. Also booking the Epcot Area resorts (BCV and BWV) during Food and Wine Festival can be difficult as member who own there usually book early.
They do not take reservations away, or give priority to, people just because they have more points.
There are times, if trying to book on shorter notice, that rooms will be available for cash and not points. This happens for several reasons:
1) Disney retains a small percentage of ownership for maintenance. If the rooms they own are not needed to switch member into for maintenance reasons, they are made available for cash.
2) Member trades. If a member trades from
DVC to a non-DVC resort, a cruise,
Disneyland, Adventure by Disney or oher option then a room is made available to cash to offset the cost of the trade. Technically this room is already reserved on points by the member, but is traded. It can not be reserved on points twice.
3) 60 day window. At 60 days out, any rooms not reserved by points are turned over for cash reservations. Part of the income offsets our dues as "breakage income."
Again, the key to DVC is booking early. If you normally can't plan a vacation several months in advance. DVC may not be your bast option. However, eve on fairly short otice, most people have gotten a room, just not always their choice of resorts or room sizes. OKW and SSR (and soon AKV) will likely have the most availability year round because of he size of the resort. VWL is the smallest DVC resort, BWV and BCV are close to Epcot, and these three resorts all book up fairly quickly.