I'd love to have the freedom to use various languages for the problems they work best for but I'm not sure how this can be accomplished today.
I have had a fair amount of success using web services as the language abstraction layer and that works great... but it's slower than molasses even using localhost.
Steve Yegge has talked about this very issue and how it is helping to drive further interest of VM's. On the .NET side, the last I heard there wasn't a not ugly way of communicating between the DLR and CLR. Has that changed? How are things on the JVM front? What about allowing VM's to interoperate?
BTW, I don't have any real reason to care except that I'm a nerd with nothing better to think about. :)