I for one have seen very little evidence for it other than your normal cause/effect, and certainly not across so-called "past lives". For my part, I believe it to be another way of happy-making for religionists scared of facing reality, much like concepts of heaven, etc.
I must agree with you, Daystar. Most people interpret Karma, which is the force generated by a person's actions, as simply meaning that what you do to others will be done to you. That ain't necessarily so; however, our actions can certainly bring consequences--nothing supernatural about that.