Google Patent Secrets

Many of the concepts that make a link natural were revealed in the Google Patent. In addition, the following "unnatural" suspicions about how Google used links to determine the ranking of a given page have all but been confirmed.

the Google "sandbox" or time-delay appears to be confirmed
the anchor text of the link - it should vary from link to link (as if the person adding the link to their site made up the anchor text)
links from fresh pages might be considered more important
the title of the page that the link is on
the growth rate of links to your website - the faster links are added the more they look like search engine spam
the age of any given link - older links have more credibility than newer links
the growth rate of independent peer documents - in other words other pages on the same site so don't add pages too quickly
new websites with a lot of links look very suspicious
links coming from the same class "C" address look suspicious as well

It's a safe bet that other search engine companies use or will soon use similar data to determine the value of the links. There are other factors that while not in the Google patent are also strongly believed to impact search engine results; these include:

the relevancy of other content on the page in proximity to the anchor text
the type of page the link is found on - is it static HTML or is it generated as with some existing automated link exchange applications
search engines consider sites with a lot of content more important than sites with less content
one-way links - many sites with multiple one-way links faired well during the Florida update
duplicate content - the first one found with the oldest content is considered the authority, others are pushed down in the rankings.

Managing all these factors is a great deal of work especially since you have very little control over many of these factors (title of the links pages, updating the link's anchor text, etc). Natural Link Exchange helps you manage these factors in several ways.