When you run "emerge gnome -p" if you paid attention to the output of your previous emerge command, you'll notice that it suggests adding famd to the default runlevel to have nautilus and gnome-vfs monitor file changes:
# /etc/init.d/famd start
# rc-update add famd default
# /etc/init.d/hald start
# rc-update add hald default
# /etc/init.d/mDNSResponder start
# rc-update add mDNSResponder default