Mono 2.0 is due in a few weeks now and CodeCommander JB Evain confirms that db4o runs smoothly on it.
It is now possible to checkout the db4o.net module, type make and all assemblies are compiled and working. Of the full set of db4o tests only 9 are failing out of 5127, 4 or them being x-platform related, leaving only 5 tests to fix for a perfect compliance.
Thanks JB! =)