This has been an issue as far back as a decade ago with G3 iBooks. I had my G3 800's logic board replaced twice under warranty, but it failed again after that. The 'hot coin on the gpu' trick solved the problem, albeit temporarily.

http://forums.macnn.com/69/mac-notebooks/210232/diy-ibook-du...

http://en.wikipedia.org/wiki/IBook#Quality_issues