Why reinvent the wheel? There are examples out there of how it could be done. This is one of them:
http://fallout.wikia.com/wiki/Karma_(Fallout_3) . It contains an example of how your actions bring you both advantages and disadvantages and affect the game you're playing.
I've outlined what it could be in Elite in a previous post which has drowned in this thread so I will repeat it every few pages hoping that it sparks some discussion which will in turn at least make Sandro read it.
Basically what I outlined would add a good chunk of the sooo desired mythical DEPTH to the whole game, causing you to reconsider which missions you take or what do you do, because your actions will suddenly matter in the long run, not just in the moment.
Also I think we're scratching the outside symptoms not realising what is the real cause of the problem. And IMHO the cause of the problem is that the killed player loses way much more than the killer, while also they are both (the victim and the killer) not gaining anything from that encounter, making it meaningless. And of course this also isn't exactly new -
I've written about it in detail after open livestream.

It is also semi-tied to the pace we can re-earn the rebuy, and IMHO its also the cause of combat logging.
Last but not least, I think we should differentiate two things - using trendspotting (karma) as a measure to various decisions (like deciding if somebody is a grieframmer or a logger), and using karma as a gauge of your actions towards certain roleplay. In short, combat logging has nothing to do with someone being good or evil, only a poor game player (and against TOS). Griefwinders however, do it on purpose and it should contribute to their overall "evil" status. So there is a delicate line here.
Now knowing nobody will click these links because they will be lost in this thread, I'm providing spoiler quotes:
Post 1 - Karma as a career path:
Post 2 - Invested time vs risk imbalance - karma proposal: