Michael Gerson defends the Special Olympics effort to attach social stigma to the epithet "retard". Their method seems like a sensible, proportional means to a worthy end. Here's another method, perhaps more appealing to philologists and others who hate to see language shrink because of boors: let's use the verb "to retard" in its proper sense. Not with reference to individuals, perhaps, but concepts. E.g., "My blogging habit retarded my progress in grad school."
If nerds can reclaim the word, it will become a lot less cool to use as an insult!
(If you think nerds can never salvage a word, research the history of the word "networking".)