Sounds like most of those above have the K-3 and are rightly proud of it, however they down play the K-3 II which I recently bought to supplement my K-5. Apart from built in flash, it has all the excellent attributes of the K-3, PLUS:
1. GPS - provides location and direction of your photos on google maps and EXIF.
2. Improved shake reduction - 1 stop
3. Improved focus tracking
4. Astro tracing
5. Compass and tracking
6. Pixel Shift technology - used with a tripod, it takes resolution and noise reduction to a far higher level
Pixel shift technology apart, the ISO/noise levels are identical in both cameras.
Some people use built in flash for light fill in silhouette situations, it's good for that. But in my opinion, built in flash just kills indoor shots. My camera dealer (SRS) bundled the neat little (shirt pocketable) w.r. AF201 FG with the K-3 II - its adjustable angle lets me use bounce flash. I would rather have this in my bag/pocket than carry around an add-on 0-GPS unit. At least with the K-3 II, it is possible to have both gps etc and add a flash when needed - same cant be said of the K-3 and 0-GPS.
That's my rationale, everyone has their own preferences. Hope I have added some balance to the recommendations. I am sure you will enjoy whatever you choose - a giant leap forward from the venerable K-10D.
To get an idea of the power of pixel shift watch this video