When creating a community based social site, at what point should one introduce the feature of having discussion boards? So for example a popular niche site such as IMDB has dedicated discussion boards for each actor and movie. This works well for sites that already have a solid userbase but what about ones starting from ground zero? Is there a certain amount of users you should have before implementing this sort of feature? Would simply having a system in place from the jump be enough to motivate users to create conversation with one another or would it have the complete opposite/negative affect on new and future visitors?
I would say that you should first start implementing comments (maybe Facebook comments), then look at their evolution. Try to feel if a specialized board would solve any problem the comments have.
Plus, a wide empty board does not make one want to create an account. Using a simple comments system is easier on the user, especially if they don't have to create a login.
I insist on "Facebook comments" because not forcing the users to have to create yet another login is a great starting point to get users to join. Implementing FB login or OpenID (Google) and use an existing system in place will make the users feel more comfortable, as they already know the system you'll have put in place.
Personally I think that board discussions are mostly a thing of the past, and are being replaced with Facebook and Twitter "open discussions".