I play most of my intensive games at 1280x800 on my 24" LED cinema display when it's hooked up to my macbook pro (C2D 2.66ghz 9600m). There's not a lot of recent 3D games that can be run at 1920x1200 for my macbook pro.
For example, I tried to play Red Alert 3 on 1920x1200, and Even if I turn all of the settings down to the lowest (which makes it look horrible), the game laggs a bit. Now, when I changed the resolution to 1280x800, Even at medium settings the game is playable.