Dr. Donna Malayeri [1], a researcher on EPFL's Scala team, has published a landmark paper [2] that got accepted for publication in the renowned SIGBOVIK [3] conference series. The paper presents the most lucid criticism so far of Scala's "Pimp my library" pattern for API extensions. For the interested, SigBovik 2010 proceedings are available as a free download (http://sigbovik.org/2010/
Links:
[1] http://www.cs.cmu.edu/~donna/
[2] http://www.cs.cmu.edu/~donna/public/pimp-my-library.pdf
[3] http://sigbovik.org/2010/
[4] http://sigbovik.org/2010/proceedings.pdf