I am using openSUSE 12.1 and MonoDevelop (2.* and 3.*) displays an exception dialog at startup saying /MonoDevelop/Core/PlatformService experienced a problem. In fact, if you launch MonoDevelop from the Terminal (execute monodevelop at prompt), more information will be displayed.
So the conclusion for me is simple, that MonoDevelop failed to find libgnomeui.*.so on this machine, which can be easily fixed by installing this package libgnomeui,
zypper install libgnomeui
You may hit another problem, but the message got from the Terminal should be your guide.