I made the same mistake (clicking "do not show again" in NM applet) as this guy: Where can I find network manager's gconf key?
The problem is that the entirety of my nm-applet/gconf.xml is:
<?xml version="1.0"?> <gconf> <entry name="stamp" mtime="1361807727" type="int" value="3"/> </gconf>
So the only listed key is "stamp". I will manually add a new key "suppress-whatever: false" in gconf-editor, but I don't know the name of the key to add.
gconftool-2 --recursive-list /apps/nm-applet
only shows existing keys, i.e.:
stamp = 3