I think it really depends on
what kinds of diagrams and images you're trying to use. I've
been using embedded dot (GraphViz) diagrams with org for a
number of years, and I find it fantastically helpful for
things like graphs (nodes connected by arrows, optionally all
labelled), data structure diagrams, etc. ... the basic boxes
and lines kind of drawing.
I also just discovered ditaa,
which seems also good for boxes and lines, but with more
freedom (and more work to edit the input).
I've also used PlantUML for
modelling diagrams.
I know others are using embedded
R code to get data visualization graphics automatically.
Most of these use separate
packages to create the graphics, but there are hooks in org to
call the external programs and include the results in the
document.
-pd
--
Peter Davis