Enter social networking sites like Facebook. Individuals and organizations using the site to be a part of and engage virtual communities/social networks can get a great deal of value out of Facebook. If Facebook were to go under, it would be annoying, but life would go on. I try not to get too invested in any social media, although I do have hundreds of indexed pages on Blogger.
I think there is a danger of organizations being over-reliant on any third-party technology. One danger is the site going under. While Facebook is finding a path to cash, I still have concerns about its long-term viability. Although, even if Facebook hits hard times, it won't disappear overnight. That said, if an organization is reliant on Facebook to connect with its "community" and Facebook declines, decisions need to be made about where to maintain a virtual community presence.
Another concern is Facebook changing their policies or advertising rates. Organizations using Facebook are subject to the TOS, which grants Facebook a license, subject to the constraints of privacy and applications settings, to content until it is deleted by users and whomever the content was shared with. In terms of content and using Facebook as a repository of content for community-building, organizations need to understand that they lose control over content posted and Facebook makes the rules for how content is used. What gets trickier if organizations become dependent on Facebook apps, features, or contextual advertising in their business model. This shouldn't necessarily discourage organizations from using Facebook, but make sure they are vigilant about contingency plans in case Facebook policies make its use non-viable.