/. have an article about when to leave a tech job. The actual story (from here) has some remarkably good advice.
One problem I've always had is I rarely think harshly enough about my job (but at the same time, I've lost count of the times I've nearly resigned 'out of spite' ;-). I make excuses for my employers to make myself feel better about bad things. Having someone crystalise things like this is quite useful.