Rhythmbox checks for the precense of /usr/bin/gconftool-2... which belongs to >=gnome-base/gconf-2, so this should be added to the DEPEND. Also, there is a QA notice for not having doc in the IUSE. Reproducible: Always Steps to Reproduce:
gconf is implied by several other deps, so not very relevant to add. the QA notice is harmless.