I ran across this article a while ago and I thought maybe someone would be intersted in reading about it here. Here is some of the highlights
1. Do not create links too fast or too slow - too fast and it looks like it is from link farming and too slow - well google figures your not very important to too many people.
2. The age of your website is considered. You should have a proportionate amount of links depending on how long your site has been active. A site that has been active for 10 years and only has 100 links is not as good as a site that is new and has 20 links. The newer site will rank more important because the older site with only 100 links will look like it is fading out.
3. Change the anchor text in your links. Do not send the same link info to each and every link trade partner. Consider what the partner's page is about and point to a relative page on your site. You don't have to make each one different but mix it up a bit.
4. The number of years for which you purchased your domain may be considered.
Confirmation of things we already knew:
1. Do not trade links with sites unrelated to yours.
2. Update your site regularly - At least once every 3 months.
3. Link farms are bad.
4. Whenever you are working on your site - build for the customer first and the search engines second.
Here is the link to the whole article.
Google Patent Bares a Bit of Its Soul LinksManager.com
Connie