I have good news for everyone that has been asking about how to get Mono on the Nokia 800,
Michael Dominik has posted a HOWTO document to build your own version of Mono from source code on the Nokia 800.
This is still a developer package to get things going. Ideally someone that understands the Debian packaging system could do the right packaging. My knowledge of Debian packages is limited to the fact that they use the ".deb" extension.