Perfect thread... I came to the forum today because I was intending to ask this question, (though I haven't actually bought a K-x).... I was considering an upgrade (sidegrade?) from my K200D to a K-x because it seemed that it would be a lot lighter, and some days my wrists just hate the K200D.
However, weather sealing is important, I'm often down at the beach and I really don't want sand and spray getting into the camera. High ISO is less important, and I guess I have got really used to having a top LCD...
Conclusion: keep using the K200D until something else really compelling comes along. Oh yeah, and buy more lenses