I've been happy with my purchases so far as well, Steam has had some great deals! So far my list looks like...

Bioshock 2
Killing Floor
Trine
Overlord Pack
Left 4 Dead 2

My only semi regret is buying Killing Floor on day 1, it was fun the first night but then Left 4 Dead 2 came on sale the following day. Anyone who has played them both probably knows Killing Floor is basically a watered down L4D so I doubt I will touch Killing Floor again now that I have L4D2.

Anyway, its been some great deals, sadly though I was already behind in my game log before all these sales hit, so this didn't help me get caught up