Used inkscape for some diagram "drawing".

I used inkscape to draw a diagram for my bachelor's thesis. Worked out nicely.

I needed a bit of a complex thing: A matrix with descriptive text along both axes and bubbles in the matrix cells with different sizes.

My conclusions:

  1. 3-variable-diagrams are hard to get right
  2. None of the freely available diagram tools can plot those without learning some stupendously complex programming language (with mostly abhorring syntax -- yes, i mean you, gnuplot!) or using some language bindings for an API
  3. Inkscape is good for diagrams if you're willing to put some effort into learning to use its tools correctly
  4. It has great features for accurate arrangement of shapes in grids and in relation to eachother
  5. The more you can leave out of the diagram, the better it will look