Not being a Mentor, (like they'd let me anyway...:t ) the Karma points are there to let the author of that post know that you appreciate their view, or that they suck. Just a little pat on the back if you will, and it can be fun. It's not a "How has the most?" knda thing and shouldn't be used to paste someone to the wall for opening up their yap before thinking. Although...
As my understanding of Karma goes, what you do comes back to you, so if you're all over someone's post or contest or whatever, lob a + karma note to them... it'll come back around to you. I'm not a big fan of the - points though there have been occasions where the author has just been a complete wack-job and the negative stuff seeks him/her out eventually, be it here or out there.
Because I want the person to know who's doing what, I make it a point to sign my karma sent and wish most others would. That's it. Check your karma level on your user control panel.
sven