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.
[Update]
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/
AppHarbor: http://unwind.apphb.com/
DeployFu: http://unwind.deployfu.com/
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/