One thing I didn't mention in my earlier post: to me, karma doesn't really make sense in "community" areas. At least where I've seen it done well, reputation was meant to serve as a means of encouraging users to help others constructively in a way that was specific to the mission of the site (in their case, automotive modification; in our case, Arduinos and electronics hacking). The idea of "reputation", either negative or positive, in the community/bar-sport/etc. areas of the forum doesn't really serve that goal: notice the quantity of negative karma being handed out just in this thread, probably because of personal disagreements rather than belief that the receiver is being unhelpful (again, see my previous point about negative reputation encouraging poor behavior in users).
I guess where I'm going with this is: what goal does reputation/karma achieve? Where I've seen it done poorly, there was usually a non-existent answer to that question. If you can't clearly define what it is that a reputation system gives you, you have no idea how best to implement it, how to handle edge cases, or how it will affect the behavior of the users.
Where I've seen it done well, there was a terse, focused answer to that question, typically along the lines of "it provides encouragement to knowledgeable users to share their expertise, and provides reassurance to the questioner that the person has been more helpful than not in the past". Assuming that's the goal, providing a "+"/"Like"/"good post" button to end-users, solely in the technical forums, is probably sufficient (while allowing moderators to reduce reputation based on antisocial behavior as an intermediate step before more harsh responses if desired). Giving end-users a simple "negative"/"bad post" button without any accountability means they'll use it without thinking, which isn't what you want; giving them a "report to moderator" button (like we already have), which implies that a human being will be looking at it, empowers people to report problems, but it also adds accountability. (And, presumably, the moderating staff can be trusted to behave in an appropriate manner, or they wouldn't have been selected for the role.
Representing it as a number also just turns it into a game; I'd be inclined to obscure the actual number into broader categories (stars, a bar graph, etc), rather than as the actual count of people who have clicked on "nice post". But that's just fine-tuning.
(If it sounds like I'm just describing how another site does it, you'd be right; it took them the better part of a decade to fine-tune their system to the point where it now works effectively, while struggling with the issue of an exploding number of users. There's value in learning from the mistakes of others.)
Anyway, my posts have been pretty long-winded, so I'll hush up now.