Another vote for the K20...
I have both the K20 and the K200. I went to the beach this weekend and took my K200 with me, but I really missed the K20, particularly when I was doing some sunrise shooting on Saturday morning and could've used the back remote control sensor when I had the camera mounted on my tripod. I tried using the front RC sensor, but got so frustrated that I resorted to using the 2 sec timer.
I also second Gus's comments about the better sensor. When I know I'm going to need to be shooting high ISOs, I reach for the K20.
While the K200 does a lot of the same stuff as the K20, many of it's features are easier to get to without having to go into the menus--metering and AF point dials, for example. It also has a second edial on the front of the camera just below the shutter button, which makes using it in manual mode a lot easier than the K200 which requires you to hold down the AV button in order to change the aperture. On the K20, one dial is set to aperture and the other to shutter speed.
I've got a local friend who's interested in buying my K200 off of me (hopefully by the end of the summer). While I've been thinking about replacing it with a K2000, I'm also considering replacing it with a K10 as a backup to the K20.
Sure the K20 is more weight to lug around, but after missing my K20 so much this weekend, I'll just deal with the extra weight next time around.
Don't worry about having a steep learning curve with the K20; it's a pretty intuitive layout. I don't know if it's just that I'm used to the Pentax system or what, but I've had a harder time figuring out how to use my dad's Canon XSi.
If the instruction manual doesn't quite cut it for you, then check out the Magic Lantern guide to the K20, as it's written to be easy to understand.
Moral of the story--get the K20 and have no regrets.
Heather