The other day I reported that Microsoft Banning Sites from Live.com For Link Exchanges, where I uncovered an email sent to a Webmaster. The email stated that a particular site was removed from the Live.com Search index because the site was "acquiring links through posting to or exchanging links with sites unrelated to your site content." The email also added that these types of links are "spam links," and is the reason the site was delisted from the index.
It struck me that this is why Google and Yahoo remain very vague when telling Webmasters why their sites are deindexed or penalized. Simply, people may look at this email and figure that exchanges links with your friends is a bad thing. If you have a personal blog about your life and you wanted to link to your dad's dental practice web site, there is nothing wrong with that. But if you do run huge link exchanges, then you need to be worried. The email sent to this Webmaster might not be clear enough to explain the difference, and get other Webmasters worried.