Despite their obvious technological superiority there's always been a problem with Macs: software availability. This extends from general software itself to some of the onliine uses: for example, the online gambling and poker sites don't all support the machines. Finding out which in fact do has always been a bit of a bother: at least until not. For now we have Mac Poker, a site dedicated to informing you of exactly who indeed does support the machine.
It's a great deal more in depth than just a listing though. They review the various sites in detail. For example, here is their review on Fulltilt Poker, and here's the one on PokerStars.
There are many more of course, and if you're looking to use your Mac to play such games online it's a great resource to get you started. As an extra bonus there's also this listing of online casino bonuses....just what you want, money saving as you start.