I had the opportunity to use the K100 for about 45 minutes today. For most entry-level DSLRs I have used they have been low on dials and buttons, like the Pentaxt, but still remain fairly intuative and relatively easy to use . Unfortunately the K100 wasn't easy to use for me, I was fairly enthusiastic at first, I passed up the familiar Canon and Nikons to try the Pentax for the novelty of it.
I don't think I got more than 6 decent exposures. I think I've just about grasped exposure well enough to be able to get a correct looking image, for some reason I found this impossible with the K100. What's even more ridiculous is I was in Av so it requires no effort. I had to constantly play with the exposure bias to try and get a good exposure.
The best thing about the camera, for me, is the ability to change ISO. Using the 'info' button I managed to discover it was set at ISO 800 but I could not find any way to change it. That seems silly; on most cameras you press one button and scroll a dial. At worst you press menu and edit it through there. The K100 wasn't this simple. I spent 10 minutes trying to find a menu or sub-menu to change it. No luck. I ended up taking it to a pro photographer friend. He should have fixed it in 2 minutes. 10 minutes later we were downloading the manual of the internet, that didn't help either. We gave up in the end, I actually tore up some flash gels to use as ND filters!
I did eventually find the owner of the camera but it was too late by then. I think so long as you read the manual you'll be fine. Apart from clunky controls it functioned perfectly well.