Well, I installed 10.4.2 on my B&W G3 this morning and everything went just well. I had to re-enable Quartz Extreme with PCI Extreme 3.1. Sadly though, CPU Director says that it isn't compatible with this version of Mac OS and has disabled itself. Luckily, the L2 cache seems to be functional, but the processor is at 800MHz for now.
Anyone else with B&Ws had problems with installing the latest OS update?