Social media is a mixed bag when it comes to backlinks. There is a modicum of value, as social media sites allow you to link to your website in your profile. However, these days Facebook, Twitter, and other social media sites mark links as 'nofollow,' meaning that they don't pass SEO value (sometimes referred to as "link juice") to the linked site. These links won't do anything to boost your site's performance in search results.
Google can’t like this. Although its great for them to have spammers out of the Wikipedias, they’re also losing a lot of very authorative input for their PR algorithm. Think about it – if every site in the world put nofollow on every link Google’s algorithm would be worthless overnight. There has been ongoing speculation as to whether or not Google ignores nofollows from certain sites like Wikipedia, something Mr Cutts has outrightly denied (but also admitted that it would be very useful to have more granular control over nofollow so that it was not an all-or-nothing situation.)
There are numerous repositories to source affiliate products and services from. However, some of the biggest are sites like Clickbank, Commission Junction, LinkShare and JVZoo. You'll need to go through an application process, for the most part, to get approved to sell certain products, services or digital information products. Once approved, be prepared to hustle.
If you want to concentrate the PR into one, or a few, pages then hierarchical linking will do that. If you want to average out the PR amongst the pages then "fully meshing" the site (lots of evenly distributed links) will do that - examples 5, 6, and 7 in my above. (NB. this is where Ridings’ goes wrong, in his MiniRank model feedback loops will increase PR - indefinitely!)
I have not at all seen the results I would expect in terms of page rank throughout my site. I have almost everything pointing at my home page, with a variety of anchor text, but my rank is 1. There is a page on my site with 3, though, and a couple with 2, so it certainly is not all about links; I do try to have somewhat unique and interesting content, but some of my strong pages are default page content. I will explore the help forum. (I guess these comments are nofollow :P) I would not mind a piece of this page rank …
Google's strategy works well. By focusing on the links going to and from a Web page, the search engine can organize results in a useful way. While there are a few tricks webmasters can use to improve Google standings, the best way to get a top spot is to consistently provide top quality content, which gives other people the incentive to link back to their pages.
On another note, I would like to express my contempt for Google and its so called terms of service regarding the legitimate acquisition of links. why should it care if links are paid for or not? Thanks to the invention of pagerank, it is Google itself that has cancelled out reciprocal linking and has stopped people giving out links due to fear of them losing pagerank, and blogs and forums are worthless thanks to the nofollow trick. so it is now impossible to get decent links organically, without having to pay for them, and those who do give out free links are considered fools. Google has brought this dilemma on itself, and yet it seems like punishing us for trying to get links other than freely! Face facts, no one is going to link to someone without getting a link in return! google has invented pagerank which is like a currency, and so people expect to be paid for links, as giving out links devalues their pagerank and so compensation is now required. It is forcing people to use underhand methods to get links, mostly the ‘paid’ variety.