I have a last generation(DLSD) 1.67ghz Powerbook that I bought from 556mjoe that he shipped to me with Ubuntu installed on it. I found it to be a pig-it was no faster than Leopard(and probably slower doing a lot of stuff). The biggest frustration for me, though, was the trackpad acceleration-or should I say lack thereof. The TP was essentially linear, so there was no fine control over movements.
I lasted about a day with it, and then swapped HDDs and installed Leopard. I still have the Ubuntu disk because I know he put a lot of effort into making everything work right and I may use it one of thee days, but I'm much happier running OSX.
Actually, my "much happier running OS X" is just a generally true statement regardless of platform