What I do personally when I rate something is to put it in a 100 star system and then convert it to a 7 star system, (I remember reading a report that a 7 star system is less ambigous than a 5 or ten star system). This is logical to me because like a 5 star system there is a clear middle star and at least a choice in ranking somethign closer to average or closer to perfect/worst.
Yes they are putting their reputation on the line when they give ten stars, but this will happen so infrequently that it will be harder to judge their overall trustworthiness.
Evaluation systems with fewer and grosser distinctions are often more credible because they are easier to monitor.
Marginal Revolution: *Spin* magazine moves from a five star system to ten.