I tried my s602 last night in our VERY dimly lit living room. It's 20'x14' and had two 60W lamps in opposite corners on and light from another 60W lamp coming through the open french doors of a much smaller adjoining room. Light bouncing off walls from another room made it enough light to read by for some, not enough for others to give you an idea. The resulting video (having not reset anything from factory defaults on the camera) was a bit dark, especially in the shadows. I viewed the video directly on the TV from the camera (nice feature) and then erased that video and filmed another one in the room the TV is in. This room is about 12'x15' and well lit by an over lamp of 75W-100W. Boy that video was pretty darn good.
An important point to remember when comparing a still camera's video (at least the s602) to a video camera is that you cannot zoom or focus or basically change anything while filming. You can change these, but not while shooting. Also, being that the unit is so small, it is very easy to get extra microphone noises since it is in such close proximity to everything else (like your finger).
By the way, with about 10 or 12 1M pictures on the 16Mb SM card, I could fit 7sec of high resolution video and sound or 20s of low res and sound. I tried the low resolution (QVGA) in the room with the better lighting and it still looked good, but seemed a slight bit darker and, of course, lacking in clarity.