Although I'm not a .NET developer I always get excited about the work DLR team is doing at Microsoft. I watched a couple of videos from various Ruby conferences where John Lam showed the progress of IronRuby and Dynamic Language Runtime in general. The latest video I saw is from Ruby conf: http://rubyconf2008.confreaks.com/ironruby.html
Despite the fact that it's not fully compatible with a standard Ruby 1.8 implementation it looks pretty good and the .NET integration is very impressive. I wonder if someone used it in some real life projects.