I have a very strict personal policy, when I install any Linux distribution. The first thing I do after installation is remove the Mono packages and everything that depends on them. People sometimes ask me why I do that. The answer is simple - If we don't want to walk quietly into Microsoft's trap, like sheep to the slaughter, then we need to avoid Mono and everything derived from it like the plague. Because a Plague is exactly what it is.
Sam Varghese at ITWire has just posted a very good article about Mono, Where, oh where, is the ECMA-compliant Mono source code?. It is worth the 10 minutes or so it takes to read it.
P.S. A couple of pieces of good news on this subject. Neither Kubuntu nor Xubuntu include Mono. Hooray! On Ubuntu (Gnome) and Netbook Edition, you can remove Mono and the packages and programs which use and depend on it with this command:
sudo apt-get purge libmono* cli-common
This will produce a list of packages that will be removed, and ask for confirmation before proceeding. Check the list to be sure it is doing what you expect.