I'm wondering what effects your Karma has in Fallout New Vegas, since they introduced the reputation with different factions?
Karma is almost non existent in the game. The only use I can see at this point is affecting which companions will follow you. For example, you cannot have Cass as a follower while you remain evil (Technically, you can because of a quest you need her for, but if you talk to her while you have evil karma she will tell you three times to get your act together before she runs off forever).
So long answer short, its strictly for companions as far as I can tell.
Karma also affects game endings. http://fallout.wikia.com/wiki/Fallout%3A_New_Vegas_endings