Make sure your URL is not parked in a Link Farm.

Periodically check the sites linking to you to make sure that your good name is not part of a “Link Farm."

"Link Farms" are fake-content directory web sites that are set up just to provide links to one another and thus to artificially boost up their search rankings.

If the search engines find your link in such a farm, even if you know nothing about it, your search ranking can be penalized.

Question: who and why would anyone park your link in such a link farm?

Answer: a business competitor or an adversary.

There are two good ways to find those sites that are linked to yours.

1) Google it. In Google's main search window type “link:www.yourdomainname.com” and click to see all the list of incoming links. Then visit them and make sure they are not link farms. If they are, write to the web master and request immediate deletion of your URL link.

2) Go to www.alexa.com and type your URL (www.yourdomain name.com) and conduct a search. Alexa will list all the web pages that include a link back to your site. In my judgement, Alexa does a deeper search and returns more links thank Google-link functionality.

If you have a blog, Technorati has the best link search engine. When you register your blog with Technorati, every time you visit your Technorati page, all the blogs that have linked to you are listed from the most recent to the oldest.