I was a PB3 user for the past year, switched to the Mac platform, and am currently testing the PB4 Mac beta.
So far, I've found that I miss some very helpful keyboard shortcuts that I found very helpful:
F6 - create child
F7 - create parent
F8 - create jump
alt-arrow - navigate from thought to thought
F2 - rename thought
I'm working on an Intel Core Duo iMac OS X 10.4.8 and I could not re-create the shortcuts using keyboard preferences. After pressing the shortcut keys, the menu bar item name blinks but nothing else happens.
On PB3, I had a great work process for creating thoughts quickly and navigating around by using the shorcuts above along with the semi-colon creating multiple thoughts.
Look forward to hearing any fixes/alternatives.