I posted ages ago about pain the front of my knees.
I tried changing from clipless to flats etc and didn't get an improvement but then realised the riding position (knees out) on the derny at work may have been putting strain on my knees so took a break from riding it at all and then when I had to ride it again just rode knees in and that problem solved itself.
Now though I have been getting out and doing more miles recently and I've been feeling a slight tightness in the back of my (right) knee.
Found a bikeradar thread that said knee pain at the back = saddle too high but it's definitely not that.
Couldn't really describe it as pain, perhaps more, discomfort? But I reckon I should try sort out whatever is causing it incase it progresses.