Does anyone know in his SEO experience if links coming from Facebook, Delicious, Digg are useful to increase PageRank on Google?
I would say NO cause most of these links are nofollow and/or stored in hidden areas (users require their account to read those pages).
But lately when searching for some business names, the 1st results on Google was the Facebook page of those businesses (that also irritated me), but I started wondering about this question.
Outgoing links from Facebook, for example, to a website are caught by a redirect script ("Are you sure you want to leave Facebook?") - these links are definitely not counted toward the PageRank of the destination site.
Internal links within Facebook (i.e. links to the Facebook page within Facebook's indexes) will not have a nofollow or robots.txt restriction, so (insofar as a search engine is concerned) the Facebook profile page will have at least a handful of inbound links; if the company's website also includes a link to the company's Facebook profile and the company's website itself has fewer inbound links than the company's Facebook profile, I can see where the Facebook page would likely show up first in the search results.
The question is, is it desirable for the company's Facebook page to show up before the company's own website in the search results?
I can't imagine too many cases in which the company would benefit from having most users land on its profile at Facebook over landing at the site it has full control over.
PR is a mathematical formula based on the link popularity of any given page. PR is "passed" by linking to another page. So, any link that links to your page will raise the PR of that page. However, nofollow links do not pass on PR and as a result will not increase your PR at all. SO, if those pages use nofollow then, no, they will not increase your PR. The same applies to web pages with redirect scripts blocked by robots.txt.
The reason why a Facebook page might rank higher then a company website is that Facebook page simply has done a better job of establishing its relevance for that search term. This may be simply because the Facebook page has more/better links pointing to it (internal links count). It may also be because the company website is poorly done and is not search engine friendly and can be outranked simply because it makes it hard for Google to determine its relevance for important search terms.
Delicious, being a site with PR8, is a good place to get links from. Unfortunately for you, they use nofollow on the submitted links. There was some mention of nofollow being dropped if enough people share the link, but that was last year and I don't think it is true anymore.
A common misconception is that Google will not crawl through nofollow links, it is just not true. The link might have no power to transfer PR, but the bot will still check it out.
So this is accepted as a good way to bootstrap new content on your website, especially if your website is being visited by the google bot rarely... Placing a link on delicious can make your content get indexed faster, since the bot is crawling delicious much more often than your website (because of their high PR).
This is a way old question but it just popped up in stream. Here is my observation on how this seems to work. PR is either made from thin air, passed to you from another site, or both.
In the case of standard followed backlinks, they generate tiny PR then pass bigger PR.
In the case of nofollow backlinks, they generate tiny PR but pass no extra PR.
I would say that yes, regardless of whether it's nofollow, links in general would help your PR. Albeit a much much smaller impact, it should still help. Obviously this doesn't apply to sites that push their backlinks through a redirect engine or shortner. If anyone here works at Google on the PR algorithm, feel free to chime in on this thought.
