I have used mine intensively for over half a year (bought it on New Year's Eve), and while I would love it was a silent as the K-7, and have a lock on the mode selector, like the K-7, it really shines when used with long lenses and in bad lighting! Mine looks a bit worn, and mine hase some dust under the matte screen - became worse when I tried to delete the little there was - other than that, no problems at all! Photokina is said to bring both a better K-7, and a better K-x, so we'll just have to wait and see!
With a short focal length lens the K-7 is better, as long as there is enough light. Especially if you add a grip!