I didn't know about ADC until after I bought my PowerBook, so I don't know what the discount would be. When I bought my 15" PowerBook G4 (1.25 GHz, Radeon 9600 64MB, 512 MB 80 GB, DVD-R) about 14 months ago, I saved $350 with the student discount alone from the student section of store.apple.com, which made the price just as good (if not slightly better) than that of a PC notebook with similar features. Since then, PC notebooks have gotten a bit cheaper while Apple PowerBooks haven't changed much in price.
Coming from a pure Windows world (with some Mac experience in college) I found Mac OS X to be.... different. But overall I am loving my PowerBook and I'm loving Mac OS X. But I still love Windows XP too.
iBook 14" is overpriced and has a crappy screen. iBook 12" is compact and is a great value. It's also a pretty good performer, it's just a hair less powerful than Mac Mini.
PowerBook is much more powerful than iBook, but it's still limited by the aging G4 technology and the G4's slow FSB. But PowerBook is still a great machine. As time goes on I've been using my PowerBook for more and more tasks. Of course it's great for presentations with
Keynote and for
MS Office 2004 but I've also been using the bundled
iLife applications for sorting my photos, editing my home videos, and authoring menus and burning my videos to DVD. I was able to buy
Final Cut Express with my PowerBook for an additional $99, it has a thousand more features than I'll ever use, but it's more flexible than iMovie. I use both. I also love the fit and finish of the PowerBook, and the backlit keyboard is great!
Overall performance with my 1.25 GHz PowerBook feels a lot like my older 2.4 GHz P4 with Radeon 9600 for normal desktop and video tasks. My 3.0 GHz P4 feels faster though. The largest photos I work with are only 5 Mpixel from my digital camera, so I am able to work with them in iPhoto and Photoshop CS without any problems. Almost every filter and operation I do happens instantly. A few take a full second, but that seems fast enough for me. Movies play great with Apple DVD Player or with VLC or the awesome
Cellulo I am able to play Halo, WoW, UT2004, SimCity4, and Rise of Nations without any problems at all.
iBook vs PowerBook depends a lot on your budget and needs. PowerBook is faster, has a larger screen, and a faster GPU with more gfx ram.
Don't bother with the 12" PowerBook. The 12" iBook is almost as fast and in many cases the Radeon 9200 Mobility in the iBook is faster than the GeForce FX5200 Go in the 12" PowerBook. (iBook only has 32 MB of gfx ram compared to 64 MB in the 12" PowerBook though... so that means that the 12" PowerBook would be more flexible but not necessasarily faster at graphics)