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I think if you're going to do this it should definitely be optional. Of course some people will want to brag about their credit total, but others will just as assuredly prefer to keep theirs private, either because they don't want people to know how much money they are sitting on or because they are embarrassed about how little they have. Personally, if we had to choose between having credits on everyone's profile or nobody's, I'd prefer that it be absent.