I own both the A85 and a S2 IS. The S2 is very similar to the S3 with only minor (in my opinion) differences. Here are my thoughts for what they are worth.
Pros for getting the S3:
1. Zoom, zoom and more zoom. I can't say enough about that zoom. To me it is priceless.
2. Image Stabilization. Extremely nice feature that makes for many more clear shots. One overlooked feature of this is during video shooting. The video on the A85 is always shaky, the S2 IS is not.
3. The other features are cool too. The color feature and other little extras work well and are fun to play with.
4. The continuous shooting mode has 2 levels, regular continuous shooting (one per 1.5 seconds, maybe?) and "H" continuous mode which is a great deal faster. I don't know the specs on this, but it most certainly depends on the lighting conditions, etc.
5. The ability to buy the barrel assembly for the lens and attach filters to it if desired. This causes the camera to be even bigger than it already is though.
6. An ISO of up to 1600 (if I read that correctly) would be nicer. The S2 and the A85 only go to 400. However, if I understand it correctly, the aperture size is the real problem with point and shoot cameras in low light situations.
Cons to woning a S2 vs a A85:
1. The S2 (and I think the S3) only focuses in one spot in the middle of the screen. The A85 had multiple points (I think 9?). This was a HUGE drawback that I realized after my purchase.
2. Size. Not small anymore. That comes with the zoom, I would think. Not bad, but certainly not as easy to carry around.
3. The lens cover does not open and close automatically. The lens cover is a cheap piece of plastic that tends to fall off the end when in the bag. Hopefully they fixed this issue with the S3, but I don't think so.
4. If I knew I was buying a camera of this size and for the price, I would have saved to get a DSLR. The features that this gives you (aside from the zoom and IS) are not going to wow you as much as you may think they will.
In conclusion, my experience is that these cameras will NOT perform much better in low light situations, because they are, afterall, still point and shoot cameras. It may be a bit better than the A85 though. They are not going to provide you with much more (than the A85) other than a zoom and IS which seems to me to be precisely what you want the camera for anyways.
My advice is to not make the mistake I did and buy this camera because you think it will perform "like" a DSLR. It won't. However, it will perform as a very dependable point and shoot camera. If that is what you are after, you will not be disapointed in a year or so as I am now.
Andy
I can't wait for spring to arrive here so I can get outside & use my camera more. My more cat is seeing spots from being my inside subject all winter. 
I have never seen such offensive avitar choices in my life. ICK! SCARY!! 
