Unfortunately 5-point rating scales also face many challenges in their use, and different studies suggest different flaws with this particular methodology.First, one study using Amazon data has shown that many ratings (where the rater isn't required to add any additional information other than the rating they select) show a bimodal distribution.All of this makes rating music on i Tunes very useful.After Shannon and I wrote our Rating Systems article, I examined the ratings in my i Tunes catalog.In other words the distribution of ratings tends to cluster around two different numbers (e.g., 1 and 5) rather than offering a normal distribution where the ratings cluster around a single height (e.g., 3).
There are other possible incentives techniques as well, such as RPGnet's new XP System.
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 i Tunes, as well as many other sites and services.
Since I can't change the user interface, I've changed my behavior.
I'm also taking advantage of two other fields: "checked" which I use to give more distinctiveness to my ratings, and "play count" which shows whether or not I've listened to something through to the end.