I wasn't certain in which forum to post this, but found one other Mountain Lion post during my search, so will post here. Mods please move if it would be more appropriate elsewhere.
I'm wondering if any other Mac users are reluctant to upgrade for fear of incompatibilities with software such as avrdude? I suspect the Arduino IDE will run fine in OS X 10.8, but don't know for sure.
To anyone who has made the upgrade, is it working out OK with your AVR software?
The first time you start the IDE the OS will tell you that you need to install a JRE. It will go off and do that and then start up the app.
But the FTDI drivers and so on seem to be 64-bit clean, so the installer leaves them alone.