I'm occasionally lazy, want a quick break from coding/writing, or for some other reason want to access the windows side of my machine without switching over entirely.
I've played World of Tanks, Skyrim, and some other games via a Parallels VM, and while it's not as good as the native experience, it's perfectly serviceable.
Me too. I've played Skyrim, F1 2012 (before Mac version was released), etc. in a Parallels VM quite happily.
I play most of my games on native Mac now - Bioshock Infinite, Arkham City, Deus Ex, F1 2012, etc.
Bootcamp is an enormous pain, only to be used in emergencies.