I love the idea as well. Unfortunately, I still game on my gaming PC as the only Mac game I have is The Sims 3(universal CD, and its installed on my PC lol). I don't think a GMA X1300 would handle that too well anyway.
Welcome! To really give this thread a topic, are you as excited as I am to learn Steam is FINALLY being ported to OS X?
Honestly, I love the idea of gaming on my Mac, but the vast majority I play on a gaming laptop I keep on my desk.
I used to play WoW on my Mac, and I do play COD MW on my mac (although it's performance is no where near what COD MW is on windows in bootcamp) and a few other games, but I mostly play MW2, Torchlight, Lord of the Rings Online and the Half Life series.
I know TL is coming to Mac, as is Half Life thru the new porting of Steam, but LotRO will probably never be ported, and I doubt MW2 will get ported either