I was going to reply to this at some point to say that I have just bought a 12" PowerBook on ebay. £267 plus a fiver for recorded delivery, immaculate in box, 1.5 GHz, 1.25 gig ram, 7200rpm 100gig hd upgrade. Only issue was the battery doesn't have much of a life in it, so I got a replacement for £35.
I'm very impressed with it, bit of a bargain compared to having to use a windows machine which would have cost me more money and frustrated me every day! Its fast enough with the stuff I'm doing - word, excel, email, internet, skype, calendar stuff.
Anyone thinking about getting a really portable machine should really have a look at one of these before getting a windows netbook, they are fantastic machines and really easy to carry around, I haven't even turned my MacBook Pro on since this arrived, my only complaint with it is the keyboard, I think its identical in scale and size but for some reason I'm making loads of mistakes, but I will get used to it!
Marc