I'm running local splitscreen with two USB XBox 360 controllers on Mac OS X 10.6 by using the XBox 360 Controller Drivers from http://tattiebogle.net.
It works great, except the 2nd player controller acts like some of its buttons are mapped to 1st player still. e.g. pulling 2nd player right trigger fires the right trigger portal for 1st player, trying to high-five or wave or whatever only brings up the quick menu for first player, etc. I can change the config for the controllers within the game to make the shoulder buttons fire portals instead, but it would be nice to be able to fix all of them.
I was using the classic hacks to run splitscreen before the patch, so I played around in the .cfg files a bit, but returning to the original joy_config files doesn't seem to make a difference. Can't figure out why this is happening. Any suggestions?