Why does Gnome 3 not display files on the desktop?
I put some files in my "desktop" folder to be displayed on the screen but nothing happens, why?
just install "gnome-tweak-tool" and turn it on. You have to enable "Have file manager handle the desktop".
It's easier to set the appropriate gconf key with the following command:
gsettings set org.gnome.desktop.background show-desktop-icons true
Update Jan 2019
GNOME 3.28 has removed the ability to place files on the desktop (rationale, annoucement).
Install the "Desktop icons" GNOME shell extension (GNOME extensions website, git).