I just closed a tab in Safari on my MacBook and just out of idle curiosity tried ⌘-Z (the default Mac keystroke for “undo”). To my complete surprise and delight, Safari reopened the tab I just closed. Even better, history is preserved when you undo.
I’ve just started mucking around with Unity too, and there are a couple of keyboard shortcuts you should be aware of in the Mac version that I find time-saving. The first is ⌘-P to play the current scene. The other is ⌘-Backspace to delete an object.
Finally, if the cursor keys are a bit of a reach for you, then I discovered this useful list of emacs-based keyboard shortcuts that can be used in any Mac OS X text field. I find Ctrl-A and Ctrl-E particularly useful.