I recently helped out my ex employer with a HUGE business critical issues he had but didn't even get a thanks from him for the effort. (by helped I mean single handedly fixed an issue he and his "team" simply couldn't)
If he ever asked me to help him again I will just say no, but if he had said "thanks" I wouldn't be so harsh. Why is it that some people are like this and others go out of their way to make sure you feel appreciated for going out of your way to help?