Overall image quality produced by the S570 is very good and is actually one of the better recent Coolpix cameras I've tested. The camera lets you limit the auto ISO to either 80-400 or 80-800. If you're shooting outdoors or in a brightly lit room, I recommed putting it at 80-400. The S570 did perform well up to ISO 800 with minimal color shift and most fine detail intact, but it's at its best below ISO 400.
It can shoot at full resolution up to and including a sensitivity of ISO 3,200. However, both it and the step below, ISO 1,600, don't look good because of color shifting and yellow blotching. So while you can, in fact, keep shooting in low-light conditions, I can't say you'll be thrilled by the results.
This shot was taken at ISO 400 using Nikon's Best Shot Selector, which takes up to 10 shots and stores the sharpest one. Printed at 25 percent its size, the photo actually looks pretty good and there is no blur, which is nice. At 100 percent, you can clearly see it's less than ideal: soft with some visible fringing around his white shorts and well, good luck picking out individual blades of grass. So if you're doing a lot of action shooting, you'll probably want to think twice about getting this camera; it performs much better with still subjects.
I don't usually go in for the specialty portrait modes available on some point-and-shoot cameras, because they typically don't help things. For some reason I really liked Nikon's Smart Portrait System that receives a dedicated spot in the S570's shooting modes.