Hey!
I have a Canon Powershot A620 and a likewise S3IS and both cameras allows the use of zoom while filming. Also four AA rechargable batteries, same for both, which gives looong batterylife.
My battery-seller in Tjeckia sent me a mail yesterday, telling me that in five days AA-batteries with 3200 Mha would be available. Amazing amount of zap they manage to cram into these small batteries! Sorry, I digress, back to cameras. As for extra gadgets, there is a short alu-pipe that can be attatched outside lens, allowing different filters and macro&telelenses to be added. I have found same diameter on pipes for both cameras, thus can I use same macro&telelenses for both cameras. Only complaint regarding A620 is that the automatic lenscover croaked after a week, but it could be just for my camera.....
Otherwise I am delighted with both and recommend them without hesitation!
Mikke