My only experience with Boo is Renraku and I was able to quickly figure out the existing codebase, despite its current lack of documentation and comments, and contribute shortly after. I have used Python a lot, so I felt immediately at home with Boo's syntax, so maybe that had something to do with it, but the choice of using a really high level language to develop an OS is a good one, despite the obvious challenges to be overcome.

Renraku has come a long way in a very short time (now with the new design decisions, I expect development to progress even faster still, once the base infrastructure is in place) and I attribute this to Daekens decision to use a really high level managed language.