Originally Posted by allend
I had your problem but I am not exactly sure how I fixed it.
Check the contents of the ~/.gconf/apps/nm-applet directory.
I seem to recall some extra lines in the %gconf.xml file.
Gold star for you! That was it.
ETA: This suggestion gave me +5 Google Fu and allowed me to discover a higher-level way to do this. I'm adding it here for the benefit of anyone who comes across this in the future. You can also use the gconftool-2 command as follows:
$ gconftool-2 --type bool --set /apps/nm-applet/disable-connected-notifications false