QuakeLive works great on a MacBook. Also it does work with Safari on both Leopard and Snow Leopard just fine. Although at least on Leopard when quitting the game or doing other things it would cause Safari to crash. So far it's been ok on Snow. Perhaps they updated the plugin, and Snow Leopards crash protection in Safari should help a lot also.
Quake Live on the Mac is currently unplayable. I'm getting ~60 FPS on my 2.53GHz/4GB/13", and you can't bind mouse2 so no jumping. Playing in Windows is silky smooth, except the laptop gets too hot without smcfancontrol or coolbook