Steam games on Lion vs Bootcamp

[Totality]

Is there still a massive performance difference these days playing a game though mac OS x natively compared to using bootcamp and windows?

How do people find it? Recently picked up a mac but havent got round to boot camping it up.

 

[Totality]

Going to give it a go tomorrow at work. We have a 5GB a month download limit so unable to download much off steam. Fancy getting back into TF2 and some older games if possible.