Port 25 is running video on what they're calling "dynamic language runtime" with some innovative type system implementations at the core.

"big trick is deferred compilation ... looks a lot like linq expression trees ... backend can decide on different optimizations ... we can take the code and specialize it for the different types ... "

[1/2] http://port25.technet.com/archive/2007/04/30/python-java-ruby-oh-my-cross-platform-net-framework.aspx
[2/2] http://port25.technet.com/archive/2007/04/30/ironruby.aspx

other links:

http://www.codeplex.com/IronPython/

http://blogs.zdnet.com/microsoft/?p=404