I am wondering just how many links on the internet today occur because someone wanted to link to something because they liked the content (natural), as opposed to linking to another site to improve their traffic, serps, or PR.
There are probably more regular posters linking to outside then the typical SEO spammers. Also, since a huge portion of net that have high PR are no follow, usually that deter link spammers. I'd say less than 20% are articificial links. Also, when you talk about links, it should also include links within the same site, say, links to the site's own footer or help section on every page, since Google count links inbound toward pages, not domains for assigning of relevancy and page rank for each page.