This article is five years old but still holds true:http://www.javaworld.com/javaworld/jw-01-2002/jw-0111-ootools.html
The best editor for UML is a whiteboard. In my zeal for technology, I neglected to mention this in my first post.
Also, @blah^3: for what it's worth, I've used Rose, Visio, Argo, Kivio, Posiedon, Umbrello, and Dia, and evaluated a handful of other UML tools, and I found Dia to suit my needs best. My needs include ease of use, cross-platform capability (Win&Lin), export to eps for easy inclusion in LaTeX documents, and no unnecessarily linking to a metamodel or other CASE fluff. Free and easy to install are gravy, since they facilitate recommendation to students. Dia wins in all these categories, of the tools I have evaluated. I would like to know the relative merits of the tool you recommend. The screenshots at http://www.sparxsystems.com.au/platforms/uml_tool.html
are unimpressive: they could be mimicked or improved in any of the tools I mentioned above.