I’ve always liked the expression that something “gives off more heat than light”: in some circumstances ideas can hinder more than help. Buddhism has similar sayings. A teaching can be thought of as a finger pointing to the moon, but it should not be confused with the moon. A concept can be like a raft used to cross a river, but one should not cling to the raft once one has reached the other shore. Finally, if you see the Buddha, kill the Buddha.
I tend to view the notion of karma as one of these confounding concepts. Karma is often used in the sense of vengeance or divine justice: “karma sucks dude” seems contrary to the much more useful notion of compassion. And lest you think this is just a Western corruption, conservative Hindus and Buddhists use the idea much like an ignorant preacher blaming a natural disaster on homosexuality. (In fact, some Hindus blamed the 2004 tsunami on the growth of Christianity in India.)
However, there is an idea in Buddhism, interbeing, that after years of reflection has brought me to an understanding of what karma might mean. A practice of mine is that when I’m considering someone I do not like I think “had I been born with their biology into their circumstances, I would be just like them.” This is karma in the Zen sense: “this then that.” I like this meditation because it exemplifies interdependence, furthers compassion, and challenges the very notion of “I” and “them.” Some might be troubled that this seems deterministic, that there is no free will or accountability. As I’ve written elsewhere, even if we live in a deterministic universe we’re still accountable moral beings. And, if one is fortunate to have some measure of grace (either by birth, disposition, or even in overcoming difficult circumstances) one can affect the conditions of others for the better. (See the story of the sadistic killer Angulimala’s redemption.)