Landrum Kelly , Jun 18, 2006; 02:04 a.m.
The answer to that often depends on shutter life, although digital cameras can fail for other reasons.
I don't have the data on expected shutter life for various cameras, but I do know that, although I have a more modern DSLR, I am still shooting my old Olympus E-20 that I bought over four years ago. The lesson for me is that a lot of older cameras are not exactly obsolete, even if they are not performing like the newest creations--especially at high ISO, where Canon seems to be way ahead of Nikon. (I am not sure how good the new Sony is at high ISO.)
By the way, I dropped my E-20 about two years ago, and hard enough to bend the built-in lens barrel. The camera's internal "works" were not damaged, and I managed to get the barrel back in the round well enough to get the UV filter back on--although it is now stuck on. It can still be cleaned, however, and a polarizer that screws into the UV filter can still be added or removed as neeed.
I would look to general build and not only to shutter life. The E-20 had a good metal frame, and I just used it on June 11 at my grandson's birthday party. It shoots beautifully, and I have printed its TIFF files at 13x19 without the use of fractals--at crystal clarity.
Still, it is a noisy camera, and I mention it here only because of the durability question. If you don't go around dropping cameras, do get the data on expected shutter life for the specific cameras that you are considering.