Steam is the poorest platform for online play, I downloaded steam last night and bought black ops, but I simply wouldn't put up with the problems it was causing. The code is a joke, and not a very good one. Using steam as a platform to run online games like black ops is suicide. Just running it for the few hours I did, I got numerous errors crashing steam and even sometimes my computer. I have a amd 955 quad, and just running this crappy program loads each core to 50% or more while in a lobby. If they put the mass amounts of money into updating their platform and servers and they would have a much bigger fan base of online games that use steam.
I had heard some good things about steam, but my personal experience on multiplayer onlone games with it basically put an end to it for me.