I don't get it. Among other things, writing and documents are timeless and the need to produce them it isn't going anywhere. But if you classify internet browsing to be the definition of useful, sure, in that case I'm actually very surprised that you even stuck with them for this long.
Depends what you do with it. Using TenFourFox with FoxPep makes almost any G4 useable for basic work & browsing. I mean, as a college student I use my PB G4 12' to read documents, write stuff, connect to my Uni's website, listen to music, etc... As long as it isn't too multimedia based, PPC are surprisingly usable even with their 16 something year old hardware and 14 something years old OSs.