Steamcloud definitely sounds cool. Not only for wandering gamers, but for, say, if you've suddenly experienced a hard drive failure & don't have a recent backup. Yeah, exactly. Very nice.

"Also announced were some extra services Valve have in store later down the line, like driver auto-updating, and a means for Steam to check your PC, check that game you want to buy then give you a fairly conclusive answer on whether you'll be able to play it or not."