Speaking of the K-7, I prefer to turn off the High-ISO noise reduction (NR) and I believe that many Pentaxians do the same (OFF).
Why?
First any in-camera post-processing (PP) incl. High ISO NR takes some time and will slow done the camera, hence will increase the delay before you can shot again. Sometimes up to 2-3 s. It might not be important but you may miss a good shot!
Second I prefer to PP my shots on computer. I use Pentax Digital Camra Utility PDCU and Noiseware. I feel that the rendering of PDCU 4.33 and of Noiseware is better than the camera one, in addition of giving you more flexibility. Ultimately I tend to prefer Noiseware but PDCU 4.33 is not bad.
Hope that the comment may help...