Good question, I don't have a definitive answer but I would know it when it came. This is my second career and I can tell you that I knew when to leave the first. I can say that I have been pretty lucky in this career though so it would take a lot for me to leave. I consider my job fairly stable, I make ok money and I still love what I do. Yes, the company messes with me, the benefits suck and being on reserve is boring but I live in base, don't have any kids and have loads of free time to pursue hobbies.

My advice would be if there are enough times when you are up in the air and you can get through a whole flight without steaming too much about what the company is doing to you on the ground then stay. If it is following you around like a dark cloud wherever you go (i.e. affecting your life too much away from the job) then start looking into other things.