From a student with an iBook G4 12"
I am also a college student and my iBook is the best laptop I have ever owned. When I was buying my laptop last November, I considered the Powerbook 12" vs. the iBook 12". In the end, I realized that it was best to just get the iBook, despite it being, at the time, the "slowest" computer Apple sold (800 MHz).
I have never regretted my purchase. The processor has never seemed slow to me and I found the computer out performed my old 2.4 GHz Gateway and was terrific at the tasks that I expect out of it: Mail, Safari, Word, Powerpoint, Excel, iLife....Futhermore, it also is perfect for additional programs that I use lightly: Dreamweaver, Photoshop, Photoshop elements, etc. The form factor is also superior, in my opinion to the powerbook. I know someone who has a 12" PB and it does not look like it has held up as well as my iBook. The most I have on mine is some scratches on the outside, but I am going to order some of that buffing cream radtech sells and then my iBook will be brand spanking new again. Two more things that I am in love with (and often amazing so many others that see my computer--Apple users and Window users alike) is the ability for it to pick up a wireless network so easily and so well AND its superior battery life. When I first got the laptop in November, I got a good 6 hours out of it. Now, I get about 4.75-5.25 hours depending on what I am doing.
Another great thing about the iBook is that it is light on the pocket (as well as in hand).