A warning for heavy users of Steam on the Mac: apparently the software doesn't play well with the recently-released 10.6.4 upgrade. Valve has told users that "the recent 10.6.4 update from Apple has noticeable performance issues for NVidia graphic chip owners running high performance games," and that unless 10.6.4 upgrade is necessary, users looking to avoid performance problems with their games should stay avoid it until the problem is fixed. If you've already updated and are experiencing the issue under Steam, it's time to hit up Apple Support and let them know.
It's interesting to hear that Apple still hasn't gotten the games thing down, even after the largest digital distribution platform around has made a high profile transition over to the operating system. Hopefully Apple will fix the issue soon and those who've updated to 10.6.4 can get back to gaming at full speed.