Summary: I have used a K100d for several years and been very happy with the camera. I wanted to upgrade to more pixels and faster burst speed, but did not want to obsolete the lens, flash and other accessories I had accumulated. I initially considered the K200d, but at $700 - $750, it did not seem to be a good value. At $470 at Amazon, the K-x was a very good value. There are many full reviews on the web, I'll address only the "negatives" these reviews mention.
Summary: I have owned a Pentax K100D for over three years and acquired several additional lenses. Building on my earlier investments was important to me. While I have not really explored all the new features of my K-x, these are my initial reactions. The Kx is marginally smaller. One of the features that I liked in the K100D, a separate settings display panel has been removed. It did not take long to get use to activating a settings display on the viewing display panel.
Summary: This camera has been easy to use from day one. It takes excellent pictures. I had some trouble using the flash indoors. The pictures were to bright. Then I started using the Tv selection on the dial with a setting of 1/60. I use this with ISO 200 or 400. Indoor flash pictures are now also excellent. The live view focus is slow but I read that most(maybe all) DLSRs with live view have some problems. I just don't use it. I considered myself an average amature photographer.
Summary: I bought this camera as an upgrade for my K100Dsuper, to use as a second body to supplement my K20D, and for when I needed better high ISO performance than the K20D. It ISO 400-800 the image quality might not be quite as good as the K20, but beyond that, this camera is absolutely amazing. The Nikon D700 is still better, at four or five times the price.
Summary: So far the Kx has done great. Its ability to take photo in low light situations is great. Using the flash still is somewhat confusing to me, but I am old and it will probably take me a while to learn. I have a 35 yr old slr so there has been a lot of improvements and automation. The camera was slightly larger than expected and much heavier. I have only taken around 500 photos and have been experimenting with different settings.
Summary: Great camera and very good value. Hard to go wrong unless you really want a professional quality camera. The video recording option is a big plus. The only downside is for the new DSLR user, there is a dizzying array of options and things to learn. However, this is the same, I would suppose, with all cameras of this quality and complexity.
Summary: I can write on & on about PENTAX. I was a Canon analog user since I was 8 years old. After a 10-year interruption with my photography, it was time to get into digital. I started with a FUJI bridge camera (S9100). Looking @ Canon dSLR models did not impress me at all until I handled a PENTAX *ist DL. To make it short, PENTAX is ART. Whether its handling, vivid colors, user-friendliness, and more importantly its pictures are closest to Film.
Excerpt: Now getting some great results from the K-x. I used to shoot quite a bit on film SLR and this is my first DLSR, so a bit of a learning curve. To start with had a few issues getting consistent exposure and focus but more on that later...