My colleagues and I have a standing joke when we talk about what makes social networks/collaborations/knowledge management work - it's everyone's favorite radio station, WII FM (What's In It For Me). To be sure, there are some social/crowdsourcing applications out there that people contribute to purely for altruistic reasons, or to share things with their friends. However, the vast majority of attempts to harness the 'group collaborative', or 'hive mind' for business purposes or knowledge management have failed unless there was a clear win in the WII FM department.
Two examples of applications where WII FM makes a huge impact are del.icio.us (social bookmarking), and Dash Navigation (crowd-sourced realtime traffic). In both of these cases, there are clearly benefits to the users of the respective applications, and the participation engendered by that benefit is the main reason the systems produce good data (search and traffic, respectively). It is very rare that a large enough proportion of people will contribute to a 'group data/application store' without seeing a significant, and more importantly, immediate benefit to themselves. At this point, one might argue the Wikipedia instance, and while it is true that the crowd-sourced encyclopedia is quickly supplanting (if it hasn't already) most 'old-fashioned' references, there are intrinsic rewards that drive people to contribute to Wikipedia, not the least of which is seeing their name 'in lights'. I would argue that contributing to such efforts also helps one stumble upon other areas of interest/exploration, so that would satisfy the WII FM theory.
Also, if you look at Open Source closely, you'll also see instances of WII FM, despite the popular press's characterization of the movement as 'peace, love, free code for all'. To be fair, there are a number of Open Source projects that do exhibit those traits, but a large portion of Open Source code is still driven by the WII FM mentality, especially when big corporations become involved. 'Community goodwill' is never the primary motivation for any corporate participation in Open Source, despite what the press releases and PR spin may lead you to believe. Despite this, I believe that 'What's In It For Me' doesn't necessarily have to be a bad thing, as long as the needs of the community as a whole can be served by what certain corporations desire in the project. For the latest case of what could be an example of this, if it is pushed a little more by the big vendors, check out this Slashdot article on PC vendors 'strongly encouraging' suppliers to provide Open Source drivers. To be sure, this takes some of the onus off of the Dells of the world for support, but it also opens things up for the community to tinker/fix/enhance such drivers. In short, WII FM for both sides.
WII FM isn't bad in and of itself, but it certainly pays to be aware of it when evaluating various technologies or platforms, be they social networking/collaboration, Web 2.0, or Open Source. Understanding the ramifications of this idea can help you avoid big mistakes as you are rolling out a project, or choosing a technology direction.