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tedster - 9:09 pm on May 21, 2008 (gmt 0)
In a discussion at PubCon Matt Cutts mentioned that it was a relatively small signal for Google, and possibly useful in reinforcing a verdict of spotting spammy intent if other signs were also present.
It was mentioned in their Histoical and Age Data Patent [webmasterworld.com] and some people (especially registrars) picked up the ball and ran with it.