Groupon tried an experiment where it deindexed itself for six hours one day, in order to try to see if it could get a grasp on how much of its "direct" traffic was actually driven by organic search.

The results, as detailed by Groupon Director of Product Management Gene McKenna on Search Engine Land, are interesting and worth a read.

http://searchengineland.com/60-direc...lly-seo-195415