Since the three finger swipe has been stolen in Lion, I find myself forced to resort to the keyboard to switch between .h and .m files. Two finger swipe left and right only seems to work infrequently, and that should be for scrolling anyways.
The keyboard command should be Control-Command-Up, but for some reason this takes me out of Xcode and shows the project file in Finder.
I have checked both System Preferences, and Xcode's key bindings settings, and I can't find anything wrong. Xcode is set properly, and I can't find any conflicts.