It's the "Dreaded PBO CRASH!" again.

In my brilliance, I didn't offer a way to actually disable that feature if you needed to, so you're kind of stuck if you keep using that build. I'm not sure why it's broken on the Apple drivers, but there isn't much I can do about it but disable PBO support in the code. Luckily, it's not used for anything important at present and you won't actually lose anything from this.
Right now only my Xt builds have this fixed (unless you are using the special BtRL build). You can grab the current build from
here however. It's actually for testing fixes for an ATI driver bug, so it's going to have some negative performance issues for you, but it should fix your hang/crash problem at least. I'm going to update the same build later today with extra driver bug tests, and it won't have the same performance problem, so if you want to wait to download I'll come back and let you know when the better build is posted.