I used a Blueberry Clamshell iBook for a few years, I used an 800 MHz G3 Snow iBook for a year, and I've had my iBook G4 for nine months, and I can tell you that the G4 iBooks are much more structurally solid that the G3 Snow iBooks. That being said, the Clamshells will outlast the G4's any day in a toughness competition. The G3 iBooks seem to flex when you pick them up, and the bezels creaked and were never quite lined up snug where they were supposed to be. The plastic on the palmrests was much more flexible and "cheap" feeling that the G4's are, and the G3's often had problems with cracks forming in the palmrests and the corners of the bezels. The G4's are much more snug and solid-feeling. When I'm referring to the G3 iBooks, I'm only meaning the later ones with the grayish plastic palmrests. I can't speak for the earlier ones with the silvery palmrests, because I never owned one. The Clamshells are by far the toughest, though. They were engineered so that every part fit actually snapped together with significant force. They used fewer screws because of their odd shape and the way the plastic fit together.
