How many people believe that what you do has some sort of come back? What goes around comes around?
That if you do good, it will come back to you sometime somewhere?
That if you do bad - it will rebound on you - sometime - someplace?
Is there a cosmic force that brings about some sort of justice and balance in the universe we live in?
Or is there nothing? No cosmic justice for those who got none in this world? No recognition for the little bits of good you do when no-one sees? No come-back for the evil?
Yes I believe in Karma, No I don't believe that Karma is a cosmic or supernatural force. It is not carrot and stick it is just a skillful life as opposed to an unskillful one.
I think the best way I could explain my view of Karma is that doing bad things is to do unskillful things. It is kind of like trying to swim against the tide. To steal lie and do bad things is to go against the flow of life and the majority of humanity, sooner or later it will go tits up.
If you are happy, helpful, loving and do good things then people will want you around, your life will go smoothly and good things will happen.
Add into that your conscience (If you have one ;-) As Thich Naht Hahn says, your mind is like a bank. If you deposit good deeds you get good thoughts and they create a positive attitude, if you deposit negative thoughts...Well you get the idea
If I do things that are offensive to my conscience I feel pangs of guilt whenever I recollect those things. It's kind of like instant Karma.
Also those pangs of guilt are negative energy and emotion, negative energy and emotion holds you back and feeds unskillful behavior.
Your bad habits then snowball and your life can become a shitstorm.
That's my secular view of Karma.