I think it would be great if we had some kind of legend for every possible notation. For example
- 1 Star : Very Bad
- 2 Stars : Bad
- 3 Stars : Okay
- 4 Stars : Good
- 5 Stars : Perfect
The legend could be shown with a "hint" when hovering over the different star notations. I think this is very important since some people will interpret "1 star = okay" and other "1 star = very bad". Furthermore, when you have no legend, people tends to give a more "extreme" rating with a lot of "1 stars" and a lot of "5 stars". (example at the Chrome Web Store )