Was working on some articles on Unified Process and needed some diagrams. Dia is usually fine for most quick UML diagrams, but often you do need other kinds of diagrams. In my case, I needed to draw up a UP disciplines diagram and Dia tools just weren't up to it.
I could never do anything with SodiPodi, and when Inkscape came out with the promise of being easier to use, I tried it out. To my surprise , it was far more intuitive to use, and I could immediately get results I wanted without struggling with the interface. I got the draft diagram I wanted in less than 30 mins using some of the tools for the first time.
Inkscape is evolving rapidly and adding new tools all the time, so if you haven't tried it yet, you should give it a go.
One gripe though is that Dia doesn't import SVG diagrams from Inkscape well which means I lose Dia's UML information when importing Dia svg from Inkscape. I work around this by importing Inkscape PNG images into Dia for now, but it isn't a satisfactory solution.