How to design a karma reward system
JeffJenkins: What I've wanted to try but I have never had the opportunity to was having karma be accumulated on a per-topic basis.  I think any time you've got a wide set of topics this is necessary to avoid the issues of people being treated as credible outside of their domain of expertise, and it could help mitigate the issue on Stack Overflow where people who answer lots of easy questions can get much more karma than those who answer a few much harder ones.