I've been hankering after one of these for literally years, and as I need a small machine with wireless for travelling the 12" seems the obvious choice.
This is going to be a bit of a test for me to see if I like using OSX long-term. I find switching between Linux and Windows no problem, so switching between 3 operating systems shouldn't be any different. If I really like it then I'm sure I'll be laying down the cash for an Intel Powerbook once they have arrived and proved themselves. A triple boot (Linux/OSX/Win) machine sounds irresistable to me.