Mine froze once within a week of purchasing it. After that I did not see the problem for a a long time until I started shooting sports. My K5 had sensor stains on it too. I mailed it to Pentax yesterday and attached a note re: freezing as they suggested.
But prior to that there was my son's school basketball game yesterday that I was shooting. I thought I would try one last time to see if it would freeze again. 1st quarter: no problem. 2nd quarter: no problem and I am thinking, hey, maybe its not too bad...
10 seconds left in the 2nd quarter and bam! It freezes
. I do a battery pull and the camera wakes up. 3rd quarter: no problem. 4th quarter: no problem. The camera has frozen 'only' once the last 2 basketball games. Prior to that it was about 4 times a game. [I shoot only once a week for sports; just my kids; not sure how often it would be if I shot sports regularly...] The only difference between when it was freezing multiple times to now when it freezes less is the newest firmware. The battery has been showing as full whenever it has frozen.
I am waiting to see what will happen when I get the camera back. I was not very bothered by the sensor stain issue as I never shoot that kind of apertures. But the freezing is a practical problem. I can live with the freezing if it only occurs once-in-a-blue-moon as I am aware that cameras are mini computers nowadays. Reminds me of my Windows Phone from Samsung that would freeze all the time. With the Droid that I have, I have yet to see a freeze since I got it last year...Hopefully this is a software issue that can be fixed with firmware as the freezing is the only thing that I have had a real problem with as far as the K5 is concerned and if I were not shooting sports/AF-C Hi I probably would never have even seen it.