I just finished an initial port of the SharpDevelop Java support to MonoDevelop. So now those who like Java can use MonoDevelop to do simple projects. I have only tested the included projects, so beware on anything else. I did this mostly so I can get an idea of what kind of work it takes to add an additional language. Of course, it turns out to be relatively easy, at least as far as syntax highlighting and project support goes (parsing and code completion is more difficult). Perhaps I'll add a small doc to explain breifly what is required.
Perhaps someone will come along and add a way to directly use mono and IKVM instead of a java runtime and compiler which would be nice, as well as a Java/Gtk# project. (Hint: it probably won't be me)