I love my Aluminum Powerbook G4 1.25ghz 15", but I have to say I have had some serious issues with it. Granted, I bought it as a refurb, but the people posting on the Apple discussion boards prove that this isn't an isolated incident.
First, shortly after I purchased it, I had two issues. The first was with the latch not holding the lid shut. The other more serious issue was with uneven illiumination. This issue is quite serious and there are several owners of the 15" AluBook who have had their machines replaced multiple times to no avail. Finally, after the 3rd attempt to fix it, Apple has been giving them a new machine.
5 months after being fixed, my machine is having some issues again. Now, the machine is freezing up when I close the lid at random times. When I pop open the lid, the screen comes up, but everything is frozen and requires a hard boot. Also, after these hard boots, the system will take a few hard boots to come up. The first time it boots it will show a circle with a slash through it and just sit there. After a second or third hard boot it usually works.
The other issue of uneven illumination is back.
Overall, I love the machine. But there are some QA issues surrounding the 15" model. I thought that buying a refurb would help iron out the kinks but it hasn't.
Check the threads on Apple's support board and see if these issues are plaguing the second generation 15" AluBook.