Dean Calver has a version of Lua running on Xbox using XNA GSE.
I'm a big fan of unusual programming languages. I love encountering different ways of thinking about coding problems, and find that the more varied languages I learn, the better a programmer I become, no matter what language I might actually end up using.
Lua is widely used for scripting in games. I'm not entirely convinced how important that is for XNA, since C# already provides many of the features people like about scripting languages, but I find myself wondering what would happen if you tried to write an entire game purely in Lua? How well would it scale to large projects? It would be interesting to find out...
In unrelated news, the XNA Creators Club website went live this morning, including a bunch of samples written by yours truly. I'm excited!