OpenGL
I noticed that the new iPhone 3GS now supports OpenGL ES 2.0. The iPhone 3G and iPod Touches only support OpenGL ES 1.1. The guys at Engadget think that will cause the app store to splinter.
Might happen eventually but until there is a critical mass of iPhones that support OpenGL ES 2.0 it would be a mistake to cut off the rest of the user base right now.
I wonder when Google will update Android? They only support OpenGL ES 1.0 right now. Not sure what Microsoft has offhand, they keep rewriting the OS every version. Should make doing cross platform games more interesting or a bigger pain in the ass.