I bought last year, closed early in September, used the points to book a preferred studio at BWV for March 10-14/08. That was 6 months out.Wait listed for a standard view studio to give us an extra night. Waitlist came through at 30 days out.
I then added on in November and used those points to book a savannah view studio March 4-8 at AKV. 4 months out. I think that's pretty good, March is a busy time of year, but not the most busy.
I believe the problems with booking 7 months out come from wanting specific room types, specific resorts, and very busy times of year (i.e. the first 2 weeks of December through Christmas and New Year, Thanksgiving, President's Day, and I think early summer).
You shouldn't worry too much about being able to get what you want. However, if you do travel at extremely busy times, and won't be happy if you don't get your favourite resort, you should probably think about where you want to stay when you make your purchase. If you will be happy just to be at Disney then it really doesn't matter where you buy.