How do you play your games with morality choices that have a light/dark side and rep with NPC's? Are you good or bad on your first (only) play through? How often do you go back and play the game again with the opposing attitude?

I almost always play virtuously the first play through and tell myself I'll go back and try it as a bastard on the second, but I never have the motivation to replay the game. I do like to pretend I still might someday (I've yet to do my second Mass Effect run, and now I'll have a second Dragon Age run to do). I figure being a dick on the second play through makes conversations go by a lot quicker instead of playing friendly and "interested" in every dumbshit's life story.