Should I add "nofollow" to all my outbound links?
In the name of SEO we've received requests to add a "nofollow" attribute to all outbound links on a site. Unfortunately there is no definitive conclusion regarding whether this is a good or bad idea.
According to Google, nofollow links don't get crawled by their systems, and they recommend using the nofollow tag on paid (affiliate) links. We recommend you use nofollow only for affiliate links or for links to spammy sites.