I've been dual booting Ubuntu 12.04 with Win7 over a year now. As far as gaming, I played a lot of WoW with 2 characters in separate wine
instances. Doing the same on win7 would have been impossible without virtual machines and way more ram & resources used. The old thief games, system shock 2, and a lot of other older gog games run perfect under wine in linux as well. I think the experience is actually better than windows since they are in their own little wine prefix (virtual environment).
As for new games, I am more likely to buy a new game that supports linux than one that doesn't even though I use win7 more.