I always (actually that's an absolute word, but I think it is very close to always) give positive rep points when I receive Genius Bar assistance. I mean, help in solving a problem, not necessarily chatter/discussion.
Other than that, I mainly give out rep points for posts that are both courteous and informative... as well as for obtuse, or what I find to be witty, humour. This is sporadic though.
Also, now that I have a mobile phone, I find myself reading the 'nova on the bus or ferry to work and my participation, for the most part these days, is a passive one. It is tedious to compose a post or leave a comment in a rep box using predictive text. I'd prefer to wait until I'm home to post longer posts using a keyboard.
I don't think I have ever given out neg rep, although I have been tempted. I was actually inspired to adopt this approach after I read that Jack never gave it (neg rep) out. Life is too short to be negative to others. I much prefer positive reinforcement.
Come to think of it, I wouldn't mind being able to track the reputation points I've dished out. Could that functionality be added?