In reply to keith-ratcliffe:
G10 onwards are indeed fabulous cameras - and tough.
I have used a G10 continually for work and play for over four years, have taken thousands of pictures, dropped it onto a slate kitchen floor and smashed the LCD viewfinder to pieces - repaired myself easily with a cheap spare part after watching a 'how-to' video on a well-known video hosting site - and it's just carried on firing without missing a beat. It's easily been the most durable digital camera I've owned. I think it's a superb piece of kit.
There is a potential massive drawback however. The lens curtains are engineered to a very fine tolerance- they almost touch the lens. This means that if a bit of tiny grit gets trapped behind the lens curtain - result is an irrevocably scratched lens. This is a real issue when using it for climbing as stuff will probably get caught in there at some point.
To begin with the scratches aren't a major problem - they tend to show up only on the LCD rather than the image - but as time goes on more and more scratches build up to the extent that it affects image quality and, sadly, it's finally necessary to retire the camera.
A shame, as everything else is still working brilliantly.
This isn't a rare problem in the G-series (see, for example:
http://bit.ly/Iit5S0) - but I haven't heard much about the problem since the G12 iteration so the latest models may have finally cracked the problem.
As a climbing camera, the G-series are still relatively large and heavy - the Canon S-series are probably the bees knees for this role, being easily tucked down a shirt or in a pocket. Nevertheless, the earlier ones (S-90/95/100) are pretty slippery - I'd say they really need a custom mount added (such as those from Richard Franiac which can't be recommended enough) - unless you have skin the trexture of glasspaper.
From an action perspective, it's also worth bearing in mind that up to the S110, there is quite a lag between shots - so getting a climbing decisive moment is tricky. (I understand S110 onwards that shot-shot time have improved, altho' I haven't been able to check this myself).
SO, the point of all this info is: if you were thinking of buying second hand G- or S- series with climbing in mind, I'd steer clear of the earlier models, bite the bullet and go for the more recent models.