When people ask to use my powerbook, I whip out my spare iBook, and distract them with it!
I also have another spare iBook, which has been on loan to my dad for months and months now.
If I trust them and I can't be arsed to get out the iBook, I'm not too bothered if people do a bit of minor websurfing / checking hotmail on my powerbook, but anything more than that, and it's use the iBook please.
I had to take my PB in for repair recently, and that caused a lot of cleaning up, locking / deleting sensitive files etc - who knows what a prying tech will be looking at 🙂