Jim Hugunin, the daddy of both IronPython (Python for the .NET CLR) and Jython (Python for the Java JVM) demos IronPython.
You need a dynamic programming language. You work in both .NET and JVM environments. You want to learn one bag of tricks and use it in both. BUT you want to know that you can step out of the box and access the .NET environment in its entirity (GUIs, .NET libs etc) and the Java environment (Swing, Beans and what not) in their entirity when you need to.
One word: Python.