I do not think reputation systems should be on the chain itself. In fact what should happen is that different sites (like busy for instance) should set up their own reputation systems that use blockchain data.

Well I disagree with you there, exactly reputation systems should be open. But that said, if your are going to do analytics on your database will you store it in the same database i.e. the blockchain? Is that what is normally done? I guess reputation is accumulated so that would be a yes then.