Matt Cutts wrote this in his blog which should be of interest to all webmasters here. " Some site owners over at WebmasterWorld have been discussing an issue where on Bigdaddy data centers, the site wouldn’t be crawled as much in the main index. That would result in Google showing more pages from the supplemental results for that site. GoogleGuy requested feedback with concrete details, and several people responded with enough details that we identified and changed a threshold in Bigdaddy to crawl more pages from those sites." More Here: http://www.mattcutts.com/blog/gone-supplemental/