I hate to say this, but Steam for Mac is crashy as hell right now. Also, sometimes the media servers seem to be choking on the load, but that is a bit more forgivable given the decades that game-starved Mac users have suffered...
Fortunately, Valve has pushed out at least three app updates that I've noticed (there may have been more). This kind of responsiveness is to be absolutely applauded wholeheartedly.
Unfortunately it doesn't take all of the sting out.
Minus points for a buggy release.
Plus points for working like mad to fix them.
More points for publicly attempting this venture. This is no small feat, bringing Top Shelf games to the Mac...
Steam: iTunes for Games*
*until Apple adds Games via iTunes. (No, don't quibble about what they offer; not hardly the same thing, is it?!)