In StackoverFlow and sister sites 'reputation' serve a dual purpose - person's hold on the subject matter and trust that he won't spam or vandalize.
IMHO 'trust score' need to be separated out of reputation score, and this 'trust score' should be carried over to all stack sites.
So, reputation affects how much you are trusted by fellow stackers and 'trust score' affects how much you are trusted by the site system.
A possible use case would be:-
Suppose I have a high reputation in StackOverflow.com but not in Serverfault.com, since it is not part of my active interests. I google and find an answer on Serverfault.com which I find to be good and want to Vote Up, but can't as my reputation is low.
Here comes the trust part. A member who understands the answer and finds it useful would only want to Vote Up, except for vandals. So in this case 'trust score' should be used.
Hope all these makes sense.