Ha! Thanks guys ... I can't take a photo right now as my bikes parked up at work, suffice it to say that the leading edge is noticeably worn down to the tune of about 1 to 1.5mm, while at the back the tooth shape appears nearly perfect. The front one also has a little play on the shaft, and the more I think about that the more it worries me!
Since I'm a newbie and about to turn 40 I'm not doing any extreme riding, so for now I'll just get a cheapo new front and be prepared to put a whole new set on in the spring ... possibly with a lower ratio, since it's 10/42 at the moment and I'm just doing everything in first (it started out as a 250, and got demoted to a 125 after the previous owner killed the piston and barrel).