Otee and a few other companies are building games with Mono as the VM for running scripts.
In Otee's case, I believe they are using some modified version of Boo. We are also assisting Second Life in adding a few features that they need in Mono for their own game.
So I hate to admit it, but I come down on the side of conventional wisdom. Write your game engine in C++. Write your gameplay in Lua. Those might not be the right answers for the next generation. I can imagine a language with better support for concurrency stealing the application domain from C++ sometime in the next decade. And C#/Mono is nipping at Lua's heels as a game scripting language already. But for now, I think the C++/Lua combination is as good as it gets.
We know about a handful of games, but we do not have an entire list; I would love to know more about people using Mono to develop their game logic and would like to work with you guys (and yes, we can keep a secret).
Although Mono is embeddable, I always got the feeling that we could improve that API, and would like to get feedback from those embedding the VM about what kind of things they would like to have in Mono to simplify the embedding and improving future embedders experience.
Updated, some cute screenshots from Unity and games built with Unity are here
If you install their web plugin (Windows and OSX only for now), you can try out some of the samples, and sample games in here.
It is a shame that it does not run on Linux, but both the Windows and OSX versions use Mono as their high-level engine.