I'm not sure if this was intended by design or not, but why did you decide to put everything into one .scala file? I know Scala allows you to define multiple objects/classes in a file but it is pretty long and it would be pretty difficult to find what I'm looking for if I were to edit anything.
Otherwise, cool project. I too am also interested in graphs and Scala, so I'll be watching your project. Have you looked at flockDB from Twitter?