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Please see http://www.youtube.com/watch?v=Ets7nHOV1Yo

Matt Cutts recommends against using nofollow this way -- now, you might want to take anything Matt says with a grain of salt, but we do know that you cannot control the flow of PageRank in this way. Your other pages will not get more PR because you have nofollowed others; instead Matt says, the PR is lost. See the video That said, a larger site might benefit indirectly from a judicious use of the robots.txt file to prevent the indexing pf pages that are not likely to end up in the SERPs and allowing more of the site's crawl time allotment for pages that have SERP value. watch?v=4SAPUx4Beh8