Scott James Remnant wrote on behalf of the Ubuntu Technical Board today defending Ubuntu's inclusion of Mono in it's default shipped package. The entire text can be read here: https://lists.ubuntu.com/archives/ubuntu-devel-announce/2009-June/000584.html
I recognize that they are in full rights to include whatever software they choose to include (as long as any licensing requirements are fulfilled) and Mono is free software. We all, at some level of understanding, realize this. The problems that arise most frequently are the patents concerning the .Net technologies. Scott Remnant addresses these concerns in the position statement.
It is common practice in the software industry to register patents as protection against litigation, rather than as an intent to litigate. Thus mere existence of a patent, without a claim of infringement, is not sufficient reason to warrant exclusion from the Ubuntu Project.
While this may be true on a grand scale, it is widely accepted that there have been problems and dire consequences with using patented technologies on open source platforms. If it were not for this precedence, Mono might be much more accepted.
My stance is that I feel that Mono should not be bundled with GNU/Linux distributions just as a precaution against litigation (again, Mono is free software but the technologies it supports is patented). I do think, however, in the pursuit of freedom, that developers must have the choice to develop software using Mono in order to bring .Net technologies to GNU/Linux. Choice is an essential freedom that mustn't be denied. This may sound contradictory to my statement that distributions should leave Mono and Mono-dependent software out of its default install. I state it this way because I feel its up to the individual to take the risk of using software based on patented technologies (that perhaps may lead to future litigation). It is much more preferable for the individual to choose to waive their rights than for a platform they depend on to choose to do so for their entire user base. This is especially important if the owner of the patented technology does choose to enforce their patent and litigate because many users will have grown accustomed to the patented technology and a void will be left, where, conversely, no void will be left if the technology wasn't initially present. My position is for protection of the users as a whole so that each user of a distribution isn't unknowingly reliant on software based on patented technologies because it came bundled with an operating system.
In short: don't bundle it, but make it available.
Mono is a tool that provides software to create and run client and server .NET applications of various platforms. One of the concerns many Free Software supporters have with Ubuntu is that it decides for us which proprietary software is good and which is bad. As one blog noted: "If Canonical is to be consistent, I should not have to a a hypocrite about some things and not others." -- specifically in regard to Ubuntu requiring you to install proprietary codecs manually (restricted-extras) but pre-loading software that is used to support a proprietary system.
Here's how to remove the offending program, courtesy of theopensourcerer:
sudo apt-get remove --purge mono-common libmono0
As theopensourcerer notes, you should check with your distribution and needs to see if removing Mono is the right decision for you. For most of us, it is.