Quote: An average canon DSLR lasts about 100,000 shots. As it's not easily possible to tell how many shots a camera has take, I'm a little nervous of buying second hand.
Unless you are looking to buy a used 1D type then I honestly doubt that shutter life is ever likely to come into the equation. If we take the mean life of the shutter to be 100,000 actuations that's the equivalent of 10,000 per annum for 10 years - just short of 200 per week - and to be honest how many of us enthusiasts really take that many shots in a week? I know I don't - and I've still got more pictures on file than I have time to process! The more average user probably isn't going to get through even that many...
Both my DSLR's were bought second hand and neither has so far given any trouble. The oldest, a D30, is probably 7 years old or thereabouts and the only age related issue (other then the 3.2Mp sensor and slow processor) is possibly a dodgy contact on the rear control wheel.
Buying anything secondhand carries a modicum of risk but if you use a reputable dealer or purchase from a source you know to be reliable I don't believe purchasing a used digital SLR is any more risky than a film one...
FWIW the only mechanical issues I've ever had are the notorious sticky shutter syndrome that affected early EOS and my 5 has the usual lack of click stops on the mode dial...