Is gaming on Mac OS X possible? I'm currently thinking about buying a 27" iMac after my current Windows computer. I know Mac OS X is awesome, but I was wondering how is gaming on this OS. What I mean is, how much of the current game releases are both on Windows and Mac OS X ? And if they are not released on Mac OS X, is it possible (performance speaking) to play them on the Windows VM ?

I know my question might not be clear. If that is so, please comment, and tell me what I explained wrong, and I'll try to improve it.

Thanks
I hate to disappoint you but I am afraid gaming on a mac is still very limited. 
Head to steampowered.com and see for your self. 

Although I believe that in the near future the major gaming publishers will see the opportunity with growing numbers of mac users and reconsider adding OS X as a platform for gaming.

Using a virtual machine is not recommended for gaming.
You can dual boot though and run Windows natively and games work fine this way. See Boot Camp