After 5 years of owning and using a Pentax K10D, I've learned something new about the camera. I had fallen into a habit of banging away with fast shutter use - since I used the back AF button instead of the half-press - the SR system is not on for many of my shots.
I did a test with the 300mm lens hand-held. I was able to see a marked improvement with shots where I paused for a second before firing the shutter. Able to get good, usable images at this focal length at 1/10 second exposure.
This will make a major difference to the number of keepers for my concert photos.