Martin Odersky , the inventor of Scala, gave an in-depth talk about Scala at FOSDEM  Feb, 2009. He explained the design concepts and rationale for key features in the language. If you are interested in Scala this newly available video  of his talk gives a wonderful insight into the scala language and why it is becoming popular. The slides and a transcript  of the talk provides a handy reference to what he covers.
FOSDEM  (Free and Open Source Software Developer's European Meeting) is a free and non-commercial event organized by the community for the community. Each year several hundred Open Source programmers from all over Europe gather together to exchange ideas, meet other committers and project leaders. All share the common goal of creating and providing Free Software. This year the meeting was held in Brussels, Belgium on the 7th of Febuary.