之前很多人利用nofollow来控制PR流动，以此来提高特定页面的权重/排名，这项技术被称为Pagerank Sculpting(PR剪枝)。之后Google修改了nofollow的规则。

　　Matt Cutts： So what happens when you have a page with “ten PageRank points” and ten outgoing links， and five of those links are nofollowed? Let’s leave aside the decay factor to focus on the core part of the question. Originally， the five links without nofollow would have flowed two points of PageRank each (in essence， the nofollowed links didn’t count toward the denominator when dividing PageRank by the outdegree of the page)。 More than a year ago， Google changed how the PageRank flows so that the five links without nofollow would flow one point of PageRank each.

　　更直观点的

　　图片来源：http://www.cnblogs.com/shuchao/archive/2009/10/14/pagerank-sculpting.html

　　所以这次Matt Cutts再次申明了：Pagerank Sculpting并不是一个好主意。

　　访谈全文：http://www.stonetemple.com/articles/interview-matt-cutts-012510.shtml

　　文章来源：http://semthinking.com/english-seo/845