I believe in karma myself... not all the time but every now and then I think it really shows that it must exist. Of course let's also be honest, it's comforting, knowing and hoping that people will always get what they deserve.
The summation of the Law and the prophets is, "as you do unto others, so shall be done to you" per the testimony of Yeshua. If you read Mt 25:31-46, you will find that final judgement will be determined on how you treated others.