Disney has already offered the "bounce-back" free dining for Sept. 08 - if you booked a return trip for Sept. 08 during your stay in Sept. 07. We're already booked oh boy!
With respect to the Free Dining being offered to the general public, it's never guaranteed. However, in past years Disney has followed this pattern. They usually offer the bounce-back option during December (at least they did last year - so the September offer this year is a little unusual), and then they offer the free dining to UK and/or Canadian residence. Once those two things have been done, Disney will usually offer the free dining to Disney Visa card holders (usually around Jan. or Feb.), and finally to the general public (I think around Mar. or Apr.). Of course one has to wonder, if Disney gets the volume of bookings they are looking for from earlier offerings, will they ever make it down the list to the general public.
Something else to consider, I've seen throughout these boards that there is growing dissatisfaction with the 2008 version of the Disney Dining Plan. That said, Disney may be prompted to offer the free dining to everyone as they have in the past.
Last and certainly not least, if you are considering a trip I highly recommend booking through Magical Journeys. They will re-book your trip if any special offers like Free Dining are released for the timeframe of your visit. They are REALLY great I love those guys.