Scala's implementation is definitely an interesting and a valuable one. I'm not debating that inheritance-based mixins are useful, they definitely are. It's just that they aren't necessarily inheritance-based, and there are many implementations of mixins that aren't, so defining it as such is at best somewhat limited and at worst misleading.
On a side note: scala's implementation, internally, is composition-based, since they compile forwarding methods to static methods into the class. They add an interface for those forwarding methods, so it can be used for polymorphism (which is what allows the fun things) but for their system to qualify as mixins, that interface is not necessary. For a very quick reference about this, you can look at http://stackoverflow.com/questions/2557303/how-are-scala-tra...
