I've been doing some mono mvc stuff on my mac (unix not linux) in the recent weeks and have found mono combined with monodevelop to be a pretty featured and useful environment.
So far in a few prototype sites I haven't yet ran into any deal breakers or major issues.
In the next few weeks I'll be deploying some sites to linux vps servers. So I'll comment on my experience.
So this answer was a long time ago and it's taken me a while to get some stuff up and running.
So my experience: mono-2.10.1 or higher is feature complete for asp.net mvc2 (mono-2.8 had some bugs that required a source compile) and it's now being used by a few cloud providers.
Running on mono-2.8 http://srvd.in/
I've found it stable and easy to develop with, like I said there were 2 annoying bugs in the 2.8 version but they are fixed in 2.10.1.
I'm happy to elaborate based on comments.
[Update] I've blogged here about deploying mono + xsp4 + nginx: http://www.thomasvjames.com/2012/07/asp-net-4-on-mono-part-2-automating-deployment/