Update: Adobe's Tinic Uro San has extensive comments and technical details, and Aral Balkan has a FAQ with commentators grumbling that Adobe is using a proprietary RTMP protocol and disabling RTSP support to sell server software.
John Dowdell follows up to clarify an important point, 'Here's the fuller quote from Tinic: "Video needs to be in H.264 format only. MPEG-4 Part 2 (Xvid, DivX etc.) video is not supported, H.263 video is not supported, Sorenson Video is not supported. Keep in mind that a lot of pod casts are still using MPEG-4 Part 2. So do not be surprised if you do not see any video." He's referring to H264 video here, in its various implementations. The Sorenson Sparc codec works in the Player, same as before. I understand how this passage could read the other way though. But the Sorenson reference in this passage is to flavors of H264, and does not affect the world's existing FLVs.'
Update 2: Beet.TV has more info, including comments by Adobe's Ryan Stewart on ZDNet and by NewTeeVee. Beet.TV also provided the interview below with On2 CEO Bill Joll on H.264, and another Joll interview Adobe's Flash Video to Play on Mobile Phones. There's yet another at Joll interview (8/23) at Seeking Alpha.
Update 3: Beet.TV also notes that Adobe Media Player has been delayed until 2008.