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I was talking to the JPD team the other day, and we were discussing the rating field as well. Basically, I was asking for having more values (although there is always a good argument about keeping things simple, i.e. don't have too many effort levels).
In any case, while we here don't have an immediate need for a rating field with e.g. 3 or 4 values, I still want to second Jean-Emmanuel's request.
I have the impression that rating fields are very powerful and still easy and fun to interact with. If Atlassian adds configuration options, namely for the number of values, and customized semantics/labels (like discussed here), the rating field will be a real killer!