I disagree with the recovery posts to some degree. Coming from a powerlifting background, I can honestly say that the idea of "overtraining" can often be anathema to progress.

True signs of overtraining are: depression, insomnia, injury. It's when the thought of doing your workout makes you want to lie down and cry. It's when your workout log shows a loss of strength over a period of weeks. It's when you train hard and don't eat enough.

Soreness is just soreness and can be worked through, especially with something like cycling. An athlete (or commuter) can be overtrained and not even be sore.

All the posts about spinning and bike setup are spot on of course.