Stupid question, but is sleep just normal PC suspend-to-RAM? Doesn't that work on normal PCs? I think I've had some games have trouble with it and graphics cards, did Valve fix that?
Yes, but it's very well implemented. In fact, it's so quick and dependable that if I'm playing a game and someone comes up to talk to me, I'll put the device to sleep rather than pausing. (Not for any particular reason, it's just muscle memory now.) I've played a dozen or so games of all types so far and have never had a problem with suspend yet, so it seems that Valve did put a lot of effort into it.