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< Desktop | Whiteboards
The idea is to provide an easy way to get new backgrounds online, without the need to install packages and whatnot.
It is an old idea, that has been implemented several times already, but never made it into the upstream background capplet for some reason. See http://live.gnome.org/BackgroundChannels
Here is a working link to Bryans musings on this topic: http://clarkbw.net/blog/category/background-channels/