I use a 15" PowerBook as my main computer (actually it's my only working computer) and I love it. I agree with Ken, the fit and finish of the PowerBook is better than ibook. To me, those white cases and keyboards of the iBook would just show too much dirt over time. I much prefer the larger display over the 12". Although it is nice and compact I felt like I'd have to squint all the time (I know you can make fonts bigger), but I wanted a bit more in the graphics dept.
I am no techie and really appreciate the ease of use a Mac offers. But in the end it is all personal preference.
