What do you believe about karma?

I've been wondering about this recently.  I'd like to believe that everything we do has a reaction and consequence.  Like a law of physics, I've always thought (or maybe blindly believed) that no good deed goes unrewarded, and that no bad deed goes unpunished.  But after taking political science and history classes, I've seen what desparate and horrible situations over 75% of the world lives in, in large part due to somebody else's fault or neglectfulness.  Take the constantly corrupt governments of South America for example- ruthless dictators, greedy puppet presidents, and diabolical generals and police officers make the lives of their countrymen a living hell with no money or education to rebuild themselves.

When bad things happen to me (bad things meaning actions done to me by other people), I like to believe that they will get theirs sometime soon, and that I won't have to worry about payback.  But, I don't know, I'm wondering now if that's just one childhood belief we all desire to cling to, and while we all sit and pat ourselves on our heads, others more wise have already learned that you have to take justice into your own hands and see to it that the guilty are punished. 

Karma calls into question our humanity, integrity and responsability.