My AAA brochure states that it is available for stays through sometime in January 2006. (Don't remember the exact date since I don't have the brochure in front of me). It's always possible that they will offer it longer, but there are no guarantees.
In my opinion, this is a great perk if you are going during a busy period, such as this summer or during a holiday season. As stated, it's only available if you book at least 2 nights at one of the Disney Hotels through AAA. If you are thinking about staying on-site, its definitely worth looking into. Now it is possible to split your stay (stay a couple of nights on-site and a few nights elsewhere); if you book your Disney hotel and purchase the passes through AAA, you should have the enhanced FP for your entire stay.