I\'ve installed R3.0 on my Mountain Lion Mac and after some trial and error the version of GTK suggested by http://r.research.att.com/ for R3.0: GTK+ 2.24.17 framework.
I want to thank all the people that contributed to a solution of this problem. Eventually I managed to fix it, after numerous trials (and late nights!). The basic methods that have been proposed are:
install GTk+ and cairo with homebrew
install GTk2 and cairo with macports
I never managed to make this work with macports, but eventually I've been successful with homebrew, after many fruitless attempts. I cleaned up my PATH that was getting a bit messy. Then I basically uninstalled X11, GTk+, cairo and all their dependencies.
I've first installed XQuartz-2.7.4.
For the installation of all the needed components I've followed the instructions found here and installed yarp using homebrew and the associated instructions. Most people may found this bizarre (I did), but installing yarp installed sequentially all the needed dependencies to make GTk+ work (obviously I tried just to install GTk+ and cairo but it never worked or eventually RGTk2 failed to compile).
I then installed (using R CMD INSTALL) GTk2, Cairo, cairoDevice and rattle from sources. After so many months trying to fix the problem I couldn't believe that everything worked!
Thanks again to all those that contributed with their effort and their research to fix the problem.
Enzo