aristotle - 4:07 pm on Jun 14, 2009 (gmt 0)

How do I know that most of these are nofollow links?

Because, as I said in my original post, these links mainly come from public forums and social networking sites. The operators of most such sites of this type have configured them so that a nofollow tag is automatically attached to all outgoing links. The members of these sites have no control over this, and when they make a post which includes a link to my site most of them probably don't even know that a nofollow tag was added, if they even know what a nofollow tag is.

I discover these links when I see them in GWT and Yahoo Site Explorer lists of external links to my site. Even though they are nofollow links, many of them still get included in these lists. After I see a new one, I sometimes go to the forum or social networking site and look at the source code. That's how I've verified that most of them are nofollow links.