I read an article last year - I think it was a Fit Chick thing in Bicycling mag - that said you should include notes on your mood in your training log, so you can identify a bad mood trend as mental overtraining and take a break/ease up when necessary.

Unfortunately I read the article after I had already done my big bike ride for the year (which for me is the Philly Livestrong Challenge), but this year I plan to take her advice. I have a bad habit of getting so stressed by all the training that by the time I get to the event, I'm cranky and crabby and ready to bite someone's head off. Within a few weeks after it's over, I decide I'm sick of my bike and don't want to ride it anymore. Hopefully this year I will be able to make some adjustments during my training so I can keep in a better frame of mind and enjoy riding more.