I've got 1.31 on my K10D. Can't comment as I must have put it on when it came out. So it obviously works
I think that stability here means that writing to different makes of cards is more reliable. I only use Sandisk Xtremes and have never had any problems with them.
If you are not getting sharp images from your Pentax lenses I feel something must be amiss. The primes are legendary for their sharpness and colour accuracy, and the 18-55 kit lens is no slouch either.
I just got my new 35mm f2.4 today, and initial snaps on the K5 are sharp right down to wide open. My Canonist neighbour is always complaining that his 50mm f1.4 is soft until f2.8; my Pentax F50mm f1.4 is sharp at f1.4 and razor from f1.7 onwards - but then it is allegedly the second best lens ever made. Personally I don't think it is THAT good, but it's certainly way above average.