I got a chance to get hands on with the Expo build.
The build number is in the high A200s, sorry I don't remember exactly (I'd say 224, but don't quote me).
New things I noticed:
Finder updates instantly when new files are created (touch foo in the Terminal for example)
When watching a fullscreen QT movie, if you move the mouse, controls appear to play, pause, rw, fw, volume and track position.
UI is getting some polish, but it's still very early in the game.