Imagine you had a website with 10 pages and each page had a Google PageRank of 6 and more. After a week, you thought that it is good to add a forum or grow your website to 1000 pages, what will happen ?

1- You may end up seeing your new pages into Google Supplemental results.
2- Your site might loose a PageRank 6+ to PageRank 4+

For those 2 reasons, I suggest you define carefully your pages in the most interlinked way and have a unique content, title, description for each of your new pages or your forums.

Of course, you should acquire more deep links to your new pages and increase the time spent on these new pages. One more additional and primary task is to have an automatic discovery site map that can include any new page you publish into your site map page.

For more information, You can give me a call at +46 768 377 477

Notes when thinking of your Google Supplemental results:
IBL’s….TBPR..in Main Index….in Supplemental….%Supp
5………1………..2………………298………………99%
10……..2………..5………………295………………98%
20……..3……….10………………290………………97%
50……..4……….50………………250………………83%
100…….5……….80………………220………………73%
1000……6………200………………100………………33%

Yes, it is a long question but the answer it is not the main page www.youtube.com but YouTube Categories page.

Google getting smarter to define a unique pagerank for each single page of your website.

PageRank 8 for YouTube.com categories http://www.youtube.com/categories

PageRank 5 for YouTube.com main page http://www.youtube.com