Currently reading all this on my IBook, and very good machine it is as well. Also have an iMac and the house has an Airport Express network. It all just works, no hassle, no messing, almost disconcertingly so. Like Evo says, found it took a few days to become second nature ... would not look back now. Only hassle is when I have to use Virtual PC and it reminds me why I am so glad I made the switch.
Apple advice for the switch
here.
Advice from goates spot on. Online banking sites that are not keen on Safari work fine with the others, and the Mac comes with IE. The iMac works fine with 256MB, but the 512MB is no bad idea. Another good idea if one has the iBook or Powerbook is getting a spare Apple optical mouse in the briefcase for when out and about.