You get 1 Karma for signing on and posting once every 24 hours.
"Karma Post"
For every TOU infraction, you get a Moderated Message. Depending on your userlevel (Karma), getting X # of modded posts results in negative Karma.
Some TOU infractions (heavy wordfilter evasion) result in more Karma loss than more trivial (off topic posts). The minimum registration age is 13 iirc.
Depending on certain board events they give a Karma modifier (X*Karma, like 1.1*K).
The more Karma you have the higher your userlevel is. You can't search until you have 10 Karma, can't delete posts until 15 Karma, and you can never edit posts. 0-75 Karma has a scaling up post restriction. Once you have 75 Karma, no more post restriction.
It's a pretty young userbase with tons of idiots who get trolled, try to troll, or are just absolutely retarded. That's why they have Karma.
I really don't see it being anything useful if (partially) ported here.
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I like Funkysouls' reputation system. You can thank people for posts, and get thanked for your post.
You can see who has thanked a post (underneath the username of the post there's a "Thank You! (#)")
Viewing (their/your) user profile you can see how many times they've been thanked, and how many times they've thanked someone.
It is pretty close to Smogon and their Luvdiscs, except theirs is topic only and you can't see for a Thank/Thanked ratio.
Both are completely optional to use on those communities, but having them in place slightly influences people to make more quality posts.