For now, people who have SC2 on Bootcamp and SC2 on Mac reported that the Mac client should be optimized. While the medium settings work well with 9600m GT and above in Bootcamp, Mac client runs smooth with all low settings.
Blizzard is currently fixing this problem (it's obvious), and they are tweaking some graphics (Open GL) so that it will run better on Mac.
Smooth FPS:
2009 MPB 13": All low settings with terrain and physics to medium. Don't forget 3D portrait! 60fps+ at start
2009 MBP 15" or higher: All medium settings will do fine. 55fps+ at start
2010 MBP 13": All low settings with Shaders to medium and 3D portrait. All medium settings runs fine, but laggy when battle occurs. 40fps+ at start
2010 MPB 15" or higher: All Medium settings runs VERY SMOOTH. Might want to have everything else besides Shaders to "High". Looks gorgeous. 60fps+ at start with All Medium. 45~50fps+ for second Graphic settings.
2010 MPB 17" highest end: All high is exceptionally crazy.
Just to let you know, these were all tested under Bootcamp. Thanks to my friends who spent 5 hours with me to install Win 7 on Bootcamp and test this.