Great machine. My 800MHz one has had the HDD replaced with a 7200rpm one and RAM up to max 1GB, with 10.4.10 on it. The combo drive is finicky, the LCD sometimes craps out, and the battery is worthless, but otherwise it still "computes" like a champ.My current machine is a 5 year G4 Titanium Powerbook 667 DVI model.
Since i've had it I've upgraded the battery to a Newertech model, put in 786MB RAM, installed an 80GB 7200rpm hard drive and upgraded to Mac OSX Tiger. Its still running strong and its for this reason that I'm reluctant to buy myself a new top of the line maxed out 17" Macbook Pro.
my current machine is a almost 3 year old 12" powerbook, and an iMac G3 that I got free a few months ago and I am not sure how old it is.