Do you have a friend with a PC that can play games at 1920x1080 or higher res?
It might be easier to make your decision after viewing the difference firsthand.
I have a friend with a computer that can max out ANY and ALL games ever made, even Arma II, which is pretty demanding. I really enjoyed The Witcher 2 on his PC and the graphics were stunning, although I'd still like it more on a TV. Is 1080p a pretty good resolution? Because since that's the highest for an HDTV, I'd assume it's high for a PC as well.
@Solid_Moose,
Steam is alright, and its sales are amazing, but the actual social gaming experience pales in comparison to Live and PSN, which is why I'd rather use something else other than it.