Mid 90s, running a small store in Torquay, almost an hour on the train each way from Exeter, bored mindless by the journey, and looking for something to read that wasn't graffiti. A speedy trip into WH Smiths, and I came out with Mort. Sniggered so much all the way home that people began to move away from me in the train carriage, and have been hooked ever since. It would be hard to name my favourite book, as it changes with each read, but in the main it's probably Hogfather. Or Nation. Or Lords and Ladies. Or Men at Arms...
Our local library here in NB has all Pratchett fiction filed in the Teen Fiction area. Not sure what to make of that..