For example, with R 3.1.1 and Mac OS X 10.9.3 it seems to work mostly without trouble (tested in July 2014), but with R 3.1.2 and Mac OS X 10.10.1, the work-around was necessary again (tested in December 2014).
Certain combinations of R and Mac OS X have trouble with this ( details on the problem and instructions on how to work around it below). With some versions of R > 3.1 and Mac OS X, GTK+ now works out of the box with the following installation instructions. in installations from GitHub using devtools, try: install_github(., reload=F, quick=T). If the other package depends on RGtk2 and installation from source fails during package test loading with an error that RGtk2 could not be found, try installing without automatic reload, e.g. Note: for some reason on Windows 8, the RGtk2 package is not always recognized during compilation of other source packages, even if it can be loaded and works perfectly fine.
optional but recommended: install R-Studio.Once R is installed, you can install GTK directly from within R (details below). Additionally, I highly recommend R-Studio for working with R regularly (but the basic command line will work just fine for most applications). Installation information for R with GTK+ Windows