There's a time and a place for a decade old computer, or a poorly built computer on an abandoned architecture. Almost never is "my main computer" an appropriate time and place for it.

I mean, heck. I've got a Pentium IIIm and a Pentium 4m running Vista and 7 respectively that I pull out for specific tasks, but I would do everything in my power to avoid using them as main computers. (Although I'd sooner use my P4m as my main computer in some kind of extremely dire emergency than a PowerPC machine.)

Finding something that'll run current software, which will still receive security patches, and probably be faster than even the fastest iBook/PowerBook G4s in maxed configuration with lots of money dumped into restoration and newer/faster parts, isn't very expensive at all -- even for a good business notebook from a reputable vendor which sold in epic quantities and for which spare parts and service manuals are super easily available.