Discussion on:

Poll: Do you use language interoperability in .NET or Java?

I did this once 7 years ago. It wasn't hard at all, and it fit the problem space pretty well (working with Office COM). The setup then was that VB.Net and C# could not be part of the same build, but I could link to a DLL built from VB.Net, from C#. I got kind of interested in trying other languages, like Lisp, using a PD library, from C#, but I was still getting my sea legs with Lisp, and I never found an appropriate project for combining the two.