I had issues while on 10.8.1 and I believe v3.02 of the RME driver. MIDI was TOTALLY jacked up. Didn't even register the ports at all.
When I reported it via email and on the forum, everyone assured me that I was the only one having this problem (which I find weird seeing as how the people who did respond had FireWire units)...but then a week later they released HDSPe driver v3.04...0_o
I've since gone back to 10.7.x and although I've upgraded the RME driver to v3.03, I'm deathly afraid of re-upgrading to Mountain Lion just because of what happened to me the last time.