I just purchased a casio ex-s500 and the anti-shake technology works great! When I bought the camera, it was defaulted to off, but once I turned on the anti-shake feature I noticed a real difference.
Final question - does it lower the overall quality of the pictures in any way? Anti-shake works by slowing down the refresh rate on the lens, so it doesn't pick up tiny tremmors. You wouldn't notice any difference in the refresh rate because the screen doesn't delay! Professional photographers recommend you use the viewfinder anyway because it gives a true image, whereas the screen doesn't always. Regarding your other question, it can sometimes lower the quality slightly because it can pixelate (go blocky) because of the slight time delay. It is however VERY unlikely you will ever notice this! There are 2 types of antishakes:
Digital and optical.
Optical (like the ones used in Panasonic Lumix range) do it thru mechanics and provide very clear images.
Digital antishakes (like casio ones) do it thru software. While this works to an extent, it does degrade the quality of the images somewhat (it does it by increasing the ISO and dropping down the resolution) so you may end up with a "noisy" picture.
So Yes, unfortunately it does lower the quality of your picture (although you may only notice it if you decide to enlarge your photos) | 