A message board, such as GFY - "IS" a Social Networking Site, it's as Going Social as it gets, heck the bbs started the social Internet.
While I agree having them on the locked forums (unless the bot is allowed in) is a bit funny. It really is a more about promotion, really no different than me sharing a GFY URL with some friends on ICQ (which bump posts, cause friends do that on social sites). While on ICQ I know they read GFY, on a site like Twitter you could have a following of industry people and so could they, that may or may not know about gfy or forgotten about it, they could share it too and grow the viewing.
If you promote a hot topic to your social group, it could lead to more qualified readers here that are forced to signup rather than just hover and go. Outside of that, not all forums are locked from view, allowing you to easily socialize your links and give you backlinks to your post, which helps give it value as a backlink to your sites. Friends do like to share things a bit more than a bunch of strangers that some bot snagged for you.
I do find it funny that we're on a social networking site, knocking social networking sites, hehe
