Once you've used the longer zoom of the S2 IS (and its image stabilization) you won't want to go back to only 4x. There isn't that much difference in price between the A620 and the S2 IS. If you really want a pocket size camera, the S2 IS isn't one, but it's a very comfortable size to handle. Unless you're planning on making very large prints, the difference between 5 megapixels of the S2 vs. 7.1 megapixels of the A620 is insignificant. A couple people have mentioned the A610, but that's not what you were asking about.
The movie mode of the S2 is excellent, as is its sound - as others here have already attested. That was one of my main reasons for buying the S2. I didn't want to have to carry both a still camera and a camcorder. I still have a camcorder, and use it when I know I'll want to shoot more than a couple minutes or so, which isn't very often.
Good luck making your decision. :-)