I think this is not relevant in GNOME 3, which no longer has applets. Instead, you write extensions. There are multiple simple examples at http://blog.fpmurphy.com/2011/04/gnome-3-shell-extensions.ht...

Not specific to the GNOME environment, but some people might want to check out dzen if they are interested in piping CLI commands to their desktop.

http://sites.google.com/site/gotmor/dzen