text: Running Unity from the command line has a few benefits. And its easy:
  UNITY_VERSION=4.6.7p4 BRANCH=trunk /Applications/Unity$UNITY_VERSION/Unity.app/Contents/MacOS/Unity -projectPath /Users/chris/Projects/MyProject/$BRANCH/unity_project
  - Open multiple projects!
  - You can specify a Unity version (I usually immediately rename Unity to Unity$VERSION due to needing multiple versions of Unity installed).
  - You can open up multiple branches of a project at the same time easily and compare/copy things quite easily.
  - Ctrl-C will immediately kill a hung Unity. Then press the Up Arrow and Enter to get back in the zone.