Personally I don't think such a system would solve the problem I think you are trying to solve (helping companies to distinguish good Perl programmers from bad ones).

I don't think HR people / management would use such a system if it was available since they would probably not be aware of it's existance. And if there are aware of it they would probably and understandably by concerned with the quality and authenticity of the recommendations. I think they would be much more interrested in some sort of certificate, but you have already stated that you don't want that.

If the hiring process involves technical people the system might be used, but we already have other ways of finding out if someone are any good or not. I know I would be very sceptical to the recommendations given.

I think that the recommendation / rating-system might be useful for finding good talent instead of when people are applying for a position. Perhaps a project like Ohloh is what you are looking for?