mojoPortal compiles fine for me and generally works on Linux. I use OpenSuse 10.3 with Mono compiled from svn head. We have MonoDevelop projects in parallel to Visual Studio projects and I use MonoDevelop to compile it in order to create the Mono release package. So there is really not much to do in maintaing the"*nix version of mojoPortal. When I package a release for Mono, I just take the same release I packaged for Windows and replace the dlls with the ones compiled on Linux.
There are a few things like WebParts that aren't implemented in Mono so we have compiler directives to leave out some WebPart stuff whe we build on Linux and we also can just leave out files in the MonoDeveop solution for things that don't work like WebParts.
I am generally setup to test using Mono built from svn and I don't test how things work using Release version fo Mono as much as I should. When Mono 2.0 ships I will test it but maybe you or others can help with the testing of the release version.
I don't do exhaustive testing of mojoPortal on Mono so the biggest help is if you test it and find bugs please report them to the Mono team. My understanding is that they use mojoportal for QA testing of Mono, so if you point out problems they will probably be responsive in fixing them.