Having a little problem here with a Windows XP guest.
Steam will freeze up multiple times. Not running games, only using it for chatting. I've tried setting it to Realtime priority in the guest OS but that didn't help.
What happens is that it just stops responding. The windows will still be there (buddy list, any open chat windows) but they won't update, and I won't be able to see any messages I receive.
Ubuntu 9.10 host, Windows XP Media Center Edition guest. Usually running in Seamless Mode, though switching back to Windowed mode(?) doesn't fix the problem.