I've been using my iBook G4 since June, 2004, and never had any problems with the laptop freezing until I upgraded to Tiger OS X 10.4.4.
I have Tiger installed on an external HD. I haven't used Tiger that much yet. The biggest problem I've noticed is with iTunes, which keeps freezing. I can't force quit, and do anything at all, except restart the computer with Apple/Control Power Button.
This has happened many times. When I run OS X 10.3.9 from the internal HD, I have no problems with the computer freezing. When applications freeze, I have always been able to Force Quit, then restart the application with no problems.
I've also had problems with Webstractor 1.5.3 and the newest version of Firefox 1.5rc.1, both also causing the laptop to completely freeze.
Has anyone else encountered this same problem? Is there a fix? Thanks.