At D5, Walt Mossberg interviewed Steve Jobs. A lot of interesting talk about the business, but at the end, Jobs dropped some real news on us:
Interactivity (search, in particular), uses a TiVo-like letter grid, which is slower than a real keyboard (hey, maybe you'll be able to use your iPhone as a remote?), but when you need to locate the latest robot dances, it does the job.
Other video sources may come later, Jobs allowed.
Last week, word got out that adventurous developers had created their own AppleTV plug-in (among others) for playing YouTube videos; the plug-in is called "A Series of Tubes."