Hi Ralf good to hear from you!
I am not sure if this will work on the Mac just yet. My plan was to resolve most problems with the Linux version then turn my attention to Mac.
I am currently developing on openSUSE 11.4 (KDE) and using Ubuntu (Gnome) for testing.
PolyRectangles seem to be working OK on both those.
I suspect the problem will be down to a missing dependency. Sorry for my poor installation instructions, I will add some more detail on dependent packages (but writing a CamBam package would be even better!
I'll update the documentation page, but some more detail on packages to check...
Some other trouble shooting tips: Try starting CamBam from a terminal window using 'Mono CamBam.exe'
The terminal window will receive a lot of diagnostic messages which may report error messages.
I also had some problems with some gtk theme settings at one point.
deleting my ~/.gtkrc-2.0-kde4 file fixed that one.
I hope this helps!