Go big or go home.
If you're at MIX and reading this, you must come to our talk (Just Glue It!) that I'm giving with Jim Hugunin at 11:45 today. We will build an app on stage that uses FIVE different programming languages.
Yes, it's contrived but that's not the point. The point is to show you that cross language interop is real, and is something that we're taking very seriously. To be honest, the fact that some things "just work" is surprising even us. If you implement a new language, such as Ruby on the DLR, and you do it right, you'll find that quite a lot of the interop comes for free.
Hope to see you there!