Summary: This is probably the best S-series camera Canon has come out with (so far0. The S110 and S100 do not compare to this one in terms of picture quality and features available. I have used the Powershot G15 and G1x as well and the picture quality is almost identical. For the size of this camera, I will be using this one over the G1x any time I travel from now on. It fits perfectly and comfortably in your pocket, unlike the G1X and G15.
Conclusion: We purchased the Powershot S120 to take on our trip to France, because I did not want to carry my Canon 60D due to its size. The S120 is so easy to use and took spectacular photos - even better than some that I had taken on a previous trip to Europe with the 60D. The photos taken at night were amazingly clear and bright. This was, undoubtedly, the best camera purchase I have made.
Summary: Great Camera! I upgraded for the S90. Picture quality is great. Automatic mode works very well. Getting use to using the touch screen. The wireless feature to transfer photo images is a nice feature. It consumes batteries faster than the S90. Recommend getting extra batteries.
Summary: I got this camera a month ago and I already shot close to 1000 photos/videos. This is a very powerful camera in a small and light body. It is very versatile. The Software is better than in my (fairly) new Canon SLR. The optics are great. While most of my pics are not in any of the automatic modes, I am very pleased with the smart auto features as well. It works very well in dim light and in high dynamic range situations.