Hi,
well, this feature is important for me. I will have to generate many of those plots from a ROOT-based analysis.
The example I sent was made with Origin (the ugly manual export / import way). There is a free rewrite for Linux called SciGraphica (http://scigraphica.sourceforge.net). They show a very fancy example under http://scigraphica.sourceforge.net/images/polar.jpg. And I found a whole bunch of examples created with gnuplot (http://gnuplot.sourceforge.net/demo/poldat.html; http://gnuplot.sourceforge.net/demo/polar.html).
Thanks,
Moritz