From the Mono page:
Mono 0.20 has been released. Check out the release notes for an overview of the changes. You can get it here. There are no major features in this release, mostly bug fixes and performance improvements.
It looks like an impressive release, with remoting bits, threading tweaks, the beginnings of System.Security, System.XML fixes, Mono.Posix, lots of refactoring and bugfixing.
I’ll be upgrading my Mono install soon.