Playing poker on a mac has been a difficult proposition for online poker players. Historically most sites haven't supported Mac clients. That changed in early 2006 when Full Tilt Poker released the first fully-downloadable native mac poker software. Now many sites offer compatibility for the growing mac poker world. For instance, the largest online poker site (PokerStars) now offers a full native Mac client for OS X.
In addition to mac site software some software makers are starting to focus on the mac in their development of add-on programs. PokerTracker3 has been promised to be developed in mac format. In addition, Poker Co-Pilot is a new mac-focused program meant to work like a simpler version of PokerTracker. While both programs cost money they are easily worth their cost even for a moderately active poker player.
While this is an uncertain time for the Apple company due to the current state of the economy and the premium model which has thrived for Apple thus far, it is a great time for Apple owners in the poker world. Online poker sites have realized that affluent intelligent mac owners are great customers. And those sites have realized it's worth their while to cater to the mac market and improve the user experience.