I tend to use a lot of them on 'Underrated' or 'Overrated' instead of modding the comments I think are most worthy.
When it comes time to moderate I usually browse at -1 and try to read from oldest to newest, threaded. Typically I come across comments that add little to the debate and then I'm faced with the dilema of modding them down for a reason or just down to let other more valuable comments shine through.
The ones I find at +3 Troll are the most troublesome. I typically go through an internal discussion where I first consider that the comment is obviously interesting or it wouldn't attract that much attention and deserves a better score. If it does, should I just mod it up as 'Underrated' or should I give a reason for modding it up. A lot of those don't really seem funny/insightful/interesting to me, but as a conversation starter they have a value in that light alone. I hate to mod them up when they're already decently rated, but hate to leave them at troll. If I think they're distracting from the more important issues, is it a good idea to mod them down with 'overrated' or 'troll' or 'flamebait' since they already have a negative type of rating?
Then there is the friends help friends type of rating. If I come across a comment from someone I recognize as being generally thoughtful or insightful do I have a bias that is unfair in their favor? If I mod them up I worry that I'm doing it in part because of other comments and not based solely on this comment. Is that such a bad thing though? If I mod up a comment that might have been fairly rated at 1, then are thoughtful and insightful people encouraged to make more comments (a good thing) or am I encouraging half-baked comments?
What about all the comments that say something well but are repeating what was previously said but less clearly? Is it fair to mark them redundant? I generally avoid this since I don't want to discourage clear discussion, but I wish they would add more than a clear restatement. I tend to skip them but it nags me that they deserve to be modded up for insight and down for redundancy at the same time.
Diamond in the rough comments. These bother me less than others. In those instances where I find a comment that is particularly well stated, insightful or helpful I enjoy modding it up. I tend to skip funny since there are plenty of people who spend time modding those up, but it bothers me that I can't do more for these types of comments. I actually can find other comments the same person has made and mod those up as well to encourage them but I don't because it seems a waste of the mod points to make those comments I might have ignored otherwise more visible. I just wish I had a +3 sometimes. I'd even take a hit on karma to be able to do that.
Manipulating the system. Are you ever tempted to set up multiple accounts on slashdot and have them automatically behave like normal ones (programatically) so that you can mod yourself up and thus increase your own karma on an "I'll scratch my back and then I'll scratch my back in return" scenario? I don't because it seems unethical, but I do wonder how some comments get such high ratings when they seem so undeserving. Would it be wrong to try to identify those and mod them down in an attempt to use my own moderation to try to balance against bad moderation? I have not so far but sometimes my frustration with the sytem tempts me. I just don't know if it would be wrong or not.
What do you think of my strategies? Do you have suggestions? What do you do in the situations I outlined and why?