Started this journey off with Lubuntu 14.04 Linux with little success so decided to download and burn Lubuntu 16.04, after much faffing about with open firmware and various random crashes before even getting the OS installed I downloaded Debian 8.5.0 for PowerPC. Immediately thing started to look a lot more familiar! no more stupid GUI installed which takes ages to boot and even then just crashes!
The install went smoothly but then I ran into a little problem :(
After a bit of reading and cli action (few glasses of wine later...) I decided just to reinstall this time with KDE, I'd read somewhere online that this worked.
After all was said and done the experience was that great, the trackpad was almost unusable and I couldn't be bothered to fiddle with synaptics config.
In conclusion; I reckon Linux on this would be a great server OS for something like a Mac mini G4 but ultimately on the PowerBooks you're better off just using Mac OS X Leopard or Tiger