Got on the preview thing. Quite impressed! Everything installs like an app rather than integrated into the dash, kind of how the quiz thing worked.
Zune Video: Very impressive. 1080p instant video shouldn't work, but it does, and it looks bloody amazing.
last.fm: Pretty simple, loads up your last fm account and your stations are available. It shows pictures of the band and stuff as you listen. Doesn't work outside of the app though, so you can't listen to last.fm while playing a game. Scrobbles your stuff too. Nice, but the quality of last.fm seems really bad once you've got used to spotify.
Facebook: Pretty basic facebook, shows your status updates, picture feed and a newsfeed of status updates. Links your xbox account with your live account. Picture slideshow thing is nifty on the telly, but the status updates and stuff is a bit useless as it wont follow weblinks. No apps work of course. Not bad for pics, but crap for everything else.
Twitter: Pointless, as everything on twitter is links, and this doesn't do it.
There's a news feed thingy added too, only got dilbert and cnn at the mo, but could potentially be an rss news reader, which would be ace if you could add your own feeds. Perhaps you could fool it by changing dilbert.com in your dns?
Quite a good update, all free of course.