I see. It was £200 which was an okay price I think. It comes with Tiger which is good and I want to play around with an older version of OSX anyway.My main machine is a 1.42 GHz G4 eMac. It's still got enough power for me to complete my required tasks without much trouble, your G5 will be even better.
Physically, it's pretty likely. I've got a 26 year old Apple IIc in perfect working condition. Also a 22 year old Mac Classic, flawless. (Well, except the floppy drive but I broke that on my own.) But as a useful machine? I'd say if your needs are fairly basic, it should last a good 5 years. I wouldn't go as far as 10, I think we'll be dealing with a very different computing world that even your G5 won't be able to keep up with by then.
And to think the Powermac G5s were top of the range at some point; I guess then again anything is.
What's your favourite PowerPC Apple ever made? I'm sure the G5 will be a good machine for a few years to come teehee =P