I totally agree with Matthew. Also, the iBooks have had a recent bump (now 512MB, Bluetooth 2.0, Scrolling Touchpad and Motion Sensor as std) which have skewed Apples product lineup a bit - the 12" Powerbook would be quite a dumb choice when compared with the new iBook.

To deviate slightly, as for actually buying the thing... I'd recommend getting it from John Lewis. Costs the same as the Apple Store or elsewhere, but you get 2yr warranty, and very good customer service.