My thought is if you body does not tell you to stop (IE: stress injury, overuse injury, etc) then you aren't over training.
"Police Man" - http://www.youtube.com/watch?v=bB9-NcunsKc
"The difference between a successful person and others is not a lack of strength, not a lack of knowledge, but rather in a lack of will." Vince Lombardi
Eat, Sleep, Train!