Brush up your knowledge of type constructor polymorphism and learn about type constructor inference. These helped reduce code duplication and carve out a cleaner hierarchy for the new collection libraries. You'll better understand part of what makes the new collections tick and maybe your own code can benefit from them as well. Find out more here. [1]
Links:
[1] http://adriaanm.github.com/research/2010/10/06/new-in-scala-2.8-type-constructor-inference.html