Keith at MouseMisers has posted his experience with the new Disney Dining Reservations system, currently available only to Travel Agents:
Walt Disney World launched the long awaited online reservation system for dining reservations. Originally due in 2008, it was launched late last night, currently for Travel Agents only. No indication was given when the tool will be made available to the general public, but my guess is 2 weeks of testing should do. Currently, only reservations May 26, 2009 and after are available in the system, so the logical launch date would be May 26, 2009. I guess we will have to wait and see.
Read more of his experience–and see screen shots of the system–on his blog.