In Collective Choice: Rating Systems I discuss ratings scales of various sorts, from eBay's 3-point scale to RPGnet's double 5-point scale, and BoardGame Geek's 10-point scale. Of the various ratings scales, 5-point scales are probably the most common on the Internet. You can find them not just in my own RPGnet, but also on Amazon, Netflix, and iTunes, as well as many other sites and services. Unfortunately 5-point rating scales also face many challenges in their use, and different studies suggest different flaws with this particular methodology.
A blog on social software, collaboration, trust, security, privacy, and internet tools by Christopher Allen.