Search engines look at a variety of signals for ranking purposes, as well as spam detection purposes. This includes a site review to determine if it's over optimized, and can result in the rankings for a site being dropped to a lower position than they may otherwise occupy.
Any commercial link will be deleted and reported to Mollom as SPAM. As such, we highly recommend against including commercial links in comments. Even comments with a reasonable amount of relevancy to the subject will be deleted and reported as SPAM.