Karma is two things to me:
The thing that keeps me from getting mad at not getting a specific outcome from a specific person.
And
A third-party addon developed for World of Warcraft.
I'll be talking about the second incantation of Karma here. You'd have to find me in a more philosophical blog to be talking about the first incantation of it.
Karma The Addon, What's It Do?
Basically, it lets you award or remove "points" from other gamers, so as to remind you next time you interact with them how you already feel about them. The other gamer doesn't get notified, and there's no "Karma sharing" function as far as I know, so really, it's just for you and your own memory.
Personally, I guess I'm a bit of a snob. Certain behaviors annoy me and since this game is about fun to me, part of why I'm using Karma is to help improve my own fun and lower my frustration. Namely, I am in a large guild with my 60 now and want to have SOME kind of understanding of who I'm going into instances with so I don't go in repeatedly with people who annoy me. Mainly people who are selfish in a team situation, wanting to play like they solo instead of working with the team in a smooth way. I figure it's not too much to expect at level 60 that 'for the team' etiquette would have developed.
Where To Find It, Basics Of Use
I found the Addon here and it installs like any other Addon. To get the command list once it's installed and you're re-logged into the game, do /karma.
Unless I'm actively partied with someone, I have to manually add them to my karma list before I can give or take karma points from them. There doesn't seem to be a quick and easy way to do it from the Karma GUI (found by doing /karma window) but the command to add an online person to your Karma list is:
/karma addmember [player name]
ie:
/karma addmember Valdesta
Then from there, I tend to go into the GUI view (/karma window, find the person in question, and do the Karma rating changes manually with the slide bar. I also put in notes to remind myself why this person has been given or had karma removed. The interface is pretty self-explanatory once you get to it, I believe.
Unfortunately, this doesn't cover the whole "same person, alt toon" thing but copying and pasting isn't all that hard once you learn this is just another alt you're dealing with...
Determining Points Given or Taken
Everyone on your Karma list starts out at 50, so those below 50 are effectively "below average" in your determination, and those above 50 are "above average". I don't think Karma can go outside of the 0-100 range, either.
So then, I'll be giving points to some players and taking points away from others, and I have to figure out what my strategy is going to be for that so I get consistent, useful results over time. This is going to be the thing that takes the most mental time now that the Addon is installed. How much do I give to or take from people in terms of Karma for their actions which I personally deem to be 'for the team' vs 'for myself, screw the team'? I don't know the answer to that yet.
Right now, tho, I think I'll award 1 point for everything that makes me think "Hmm, that rocked" and 5 points for everything that makes me think "holy shit, THAT ROCKED!", and just reverse the sentiments for deductions. It'll be interesting to see how all these complete strangers online start to stack up now that I don't have to worry about ever sharing the information or doing anything about it other than avoiding instance parties with the ones who really really suck!
I'll let you know how it goes :)