This is an expanded version of my "Refactoring with Roles" talk. People don't ask me how to use roles. They're easy to use. They ask me why to use roles. That's pretty easy to, so long as you understand what's wrong with inheritance. This talk covers that.
A paper for this talk is at http://www.slideshare.net/Ovid/inheritance-versus-roles-1799996
Clipping is a handy way to collect important slides you want to go back to later.