After you install Gnome 3 you won't be able to see the Desktop icons. This is because they are hidden by the default settings. But it is quite easy to fix: run gnome-tweak-tool. Select the File Manager category and check "Have file manager handle the desktop". Now the desktop icons should be visible again.
When you run gnome-tweak-tool after installing Gnome 3 you can get the following error: => GLib-GIO-ERROR **: Settings schema 'org.gnome.shell.clock' is not installed The cause is that you are missing a schema which is installed together with gnome-shell (which is probably not installed because you are running the fallback mode). The obvious fix is to install gnome-shell. But if you want to run Gnome 3 in fallback mode you need to do some additional steps: Run the System Settings, go to System Info, Graphics and check "Forced Fallback Mode".