How Search Engines Use Links

Search engines need to decide what pages
 to include in their index. Discovering pages by
crawling the Web following links is one
way they discover web pages the other is
through the use of XML Sitemap files.

Crawl rate/frequency
Search engine spiders go out and crawl
 a portion of the Web every day.
This is no small task, and it starts
with deciding where to begin and
where to go. Google has publicly
indicated that it starts its crawl in
PageRank order. In other words,
it crawls PageRank 10 sites first,
PageRank 9 sites next, and so on.
 Higher PageRank sites also get crawled more
deeply than other sites. It is likely that
 other search engines start their crawl with the most
important sites first as well.

This would make sense, because changes
 on the most important sites are the ones the
search engines want to discover first. If a very
 important site links to a new resource.

Links play a critical role in ranking.
Page placement Is your link in the main
 body of the content Or is it off in a block
of links at the bottom of the right rail of the
 web page Better page placement can be a
 ranking factor. This is also referred to as
 prominence, which has application in
 on-page keyword location as well.

Social Media Link Creation
Some social media sites, such as,
 allow  you to link back to your own
 sites in your personal profile, and
these links are not NoFollowed .
Other social media sites that do not
 NoFollowlinks  in their public profiles
 include Digg, Propeller,Kirtsy, Technorati,
MyBlogLog, and Mixx.