Jump the gun much? The OP is just asking for other people's experiences running Borderlands 2, yet you've just assumed they're complaining and parroted the tired "it's a beta" line, which IMO is trolling as it's just about the most useless response to a thread in this forum.
You know what a beta's for, right? It's to find potential issues and to fix them, if you just tell someone "it's a beta" like it's okay for it to be riddled with problems like they should just ignore them, then how are any of those problems going to get fixed?
For the OP; I'm running Yosemite in a VM rather than from a partition, so I have issues running games anyway, but it does sound like a potential issue. We haven't been told of any graphics changes, so it may be worth reporting to Apple at
http://bugreport.apple.com; remember to include a system profile (About This Mac -> More Info -> System Report -> File Menu -> Save) and take some screenshots of issues if you can (Shift + Command + 3 or 4). How well did it run for you under Mavericks?