Page Rank is Google's way of deciding a page's importance. A page with a higher Page Rank is deemed more important and is more likely to be listed above a page with a lower Page Rank.  It matters because it is one of the factors that determines a page's ranking in the search results. It isn't the only factor that Google uses to rank pages, but it is an important one.

Google Page Rank is one of the most important algorithms ever developed for the Web. With billions of existing pages and millions of pages generated every day, the search issue in the Web is more complex than you think it is. Google Page Rank is a measure from 0 -10 that Google assigns each page on the internet based on how powerful that page is in terms of the number and quality of links coming into the page.

A page with a higher Page Rank is deemed more important and is more likely to be listed above a page with a lower Page Rank. Search engine optimization (SEO) can help to increase your web site or blog's page rank through optimizing each page that exists on your website or blog, SEO helping you with link building through off-page optimization campaigns as well. This can help you get more traffic from your target region because Google will see your site as relevant to your niche and send more website visitors your way. It matters because it is one of the factors that determines a page's ranking in the search results. It isn't the only factor that Google uses to rank pages, but it is an important one.

Very few pages have a page rank of 10, and anything above a 6 is considered very good. 

Few top website that have a 10 page rank. Oct 2013      

http://www.google.com/

http://www.facebook.com/

http://www.usa.gov/

http://www.dhhs.gov/

http://www.miibeian.gov.cn/

http://www.addthis.com/bookmark.php

http://us.cnn.com/

http://get.adobe.com/flashplayer/

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