It seems that if you steal from an npc, there's a chance that npc will send a hitman after you, even if you never got a bounty and no-one saw you do it. The hitman will have a note with the name of the npc that ordered the hit. However, it doesn't affect said npc's disposition and you will not be able to confront them about the hit attempt in conversation.
Npc's may know or suspect you murdered someone, even if you never received a bounty for the murder. However, I don't think it affects conversation options or (future) quests in any way.
Guards will comment if you have a high sneak or pickpocket level or if you are a member of the thieves guild, even if you never received a bounty for any crimes related to those skills or that faction.
So I guess you could say there is some form of karma in Skyrim. It just isn't about spirituality or cosmic justice. Npc's will just make some comments as you walk by and you get a few more random encounter with enemy npc's.
There is a karma system present in Skyrim. I'm am not sure of it's full contol over the game but i know that it effects random events. For example if you have a good karma a darkbrotherhood assassin may try to assassinate you.
Or more likely, a Dark Brotherhood assassin will try to kill you if you are not in the Dark Brotherhood yourself. I stole/pickpocketed a lot of stuff with my character, but the Dark Brotherhood still tried to assassinate me.