Here's the information posted on WDWinfo.
NEW DINING RESERVATION SYSTEM IN THE WORKS
Disney will begin implementing a new reservation system that combines dining, recreation and tour bookings.
The conversion will start on July 21, 2008 and is expected to be functioning early December. While this is taking place, the latest dining reservation date which can be booked in advance is March 22, 2009**. Once the new system is operating, it will revert to the 180 day Advance Dining Reservation window.
The exceptions to the shortened ADR booking window are Cinderella's Royal Table, Chef Mickey's and Victoria & Albert's.
** - While the official source states that ADR's can now be booked thru March 22, 2009, we are getting conflicting reports from calls to Disney Dining. It appears this may not go into effect until October 26.