Would run natively, though the latest titles might not be such a good choice given the limited GPU power of most Macs. Last gen titles such as HL2 and Call of Duty etc should run fine.
As for the second question no not at all
As said, they run just like on a PC with the same hardware.
CSS would obviously not be a problem. I imagine TF2 wouldn't be that stressing, depending on which MBP you have.
the act of setting lots of people on fire does seem to have an effect on the GPU 
I was just about to post a thread about gaming on the mac, but spotted this so one, hope I am not too far off topic...
I am well out of touch with PC gaming as have had my 360 for all my needs, but since getting the iMac I have been wondering about some games that are usually just more suited to a desktop. I quite fancy playing some resource manager style games (think thats what they're called?) Stuff like Sim City, Caesar, Roller Coaster Tycoon, Civilization etc.. Are any games made for the Macs as a platform or will I have to go the Boot Camp route?

I got a 24" imac the other day and boot camp is a case of running the boot camp assistant application in OS X, choosing how much space you want on the bootcamp partition, clicking next, inserting your XP/Vista disc and selecting restart or continue, it reboots the machine and immediately starts installing 
Is the process of getting a Boot Camp'd mac to play games quite painfull?
