A little late to this, but the guys at Steepster, a tea review site, have a fantastic post about how they overhauled their ratings system:

It turns out that the average rating for products on sites with 5-star scales is around 4.3. To us, this says that we need to dive deeper — zoom in to a level where it’s clear what the difference is between a really great tea and the best tea you’ve ever had.

There’s a lot of great thinking here. Rating scales are like identity systems in apps — easy to overlook them, but it can have a huge impact on the final product.