[Soupdragon]

Well I'm not sure you should use a tripod in conjunction with IS.
Having looked at a number of your cycling shots some of the problems (and they are minor in my eyes) is motion blur.
At least one of the pictures looks like you/the camera focused off subject.
I also think there is an issue with panning and IS lenses, I do suggest you read the lens instructions before condemning an optic of such high regard.

My best guesses anyway.