Hold up, or maybe it's too late. Logic 9.1+ still has issues for many people on Mountain Lion 10.8.1/2
Main problem is plugins with animated graphics (like EQ spectrum or level meters) causing choking/stuttering on busy projects WAY more than it would on 10.6.8 Snow Leopard. It's a problem with Core Audio.
It takes a few minutes to kick in and might not be apparent on new projects with only a couple tracks. But once it manifests on busier projects, you'll wish you had stayed at 10.6.8. I'd wait for 10.8.3 or the next Logic Update before attempting it.
If you upgraded and all is well, then