I see karma as a way to motivate more activity on the site. It turns participating into a game that you can win, which gets people's competitive juices flowing. We all love measuring ourselves against other people.
Let me be your first counterexample. I can't care less about the number attached to my account. You want to up mine? Be my guest.
Aside of this though, it is easy to get a high Karma/posts ratio. How to do it? If you know damn well what you're talking about every time you post, you will accrue lots of Karma from being informative. There are a few gurus here and they're easy to spot. They will have high Karma, whether they care or not.
Some, like me, who aren't biological data troves, are happy to expose their ignorance and ask stupid questions, and deal with occasional (and mysterious) downmods.
