Great point. This presentation showed how easy it can be to implement DI in ruby: http://onestepback.org/articles/depinj/index.html

Dynamic languages don't suffer many of the overheads with using DI. So do those with Mixins (see the Scala's Cake pattern for more on this http://jonasboner.com/2008/10/06/real-world-scala-dependency...)

This blog post says more about it: http://weblog.jamisbuck.org/2008/11/9/legos-play-doh-and-pro....