Conduct a search for literally any letter in the alphabet. Try a search for [s] in Google and the number two result, at least for me, is a Twitter username/profile.
This was pointed out in a WebmasterWorldthread. Tedster, the administrator of WebmasterWorld said:
Funny you should mention it - yes, Twitter profile names do seem to be ranking better.
Twitter, the next Wikipedia?
Forum discussion at WebmasterWorld.