Reports via WebmasterWorld show that Google's similar pages query, performed in the syntax of "related:www.domain.com" has been returning very different results.
Senior member BillyS reports, "As of late, this command seemed to report non-sense results anyway, maybe a fix is on the way." I get 10 results for a related match on this site, Google returns only 11 results, all from Google.com and Yahoo is similar. Something has changed with the related command at Google.
Forum discussion at WebmasterWorld.