I haven't touched my Fedora Core 3 machine that I tried to infect with Mono for some time now. I'm collecting information for "take two". When I have some spare time for another trip to Linuxland that is.
CodeProject has nice looking new article about setting up mono and an entire cross-platform section. (via Miguel & Marko).
Also, Sasa wrote on his blog about FC3 and Mono. Looks helpful.