A recent study conducted by Deloitte on more than 100 businesses with online communities reported by Josh Catone deals why these platforms often fail or don't meet the expectations:

"Businesses are being enticed by fancy technology. Mesmerized by bells and whistles, many business are foolishly blowing their entire budgets on technology

Lack of proper management. The Deloitte study found that 30% of online communities have just part-time employees in charge, and most have just a single PR person running the show. (...) Managed communities are a lot less likely to grow organically the way general mainstream social networks do, so you need someone who knows how to build one in charge.

The wrong measurement metrics. Moran noticed that most businesses are measuring the success of their communities in the wrong way. Though their stated goals are usually to create viral, word-of-mouth marketing and increase brand loyalty, the metric they use to gauge success is unique visitors. If all you’re after is growing visits to the site, then you’re missing the point. You’re not trying to compete with mainstream social networks, so you don’t need to chase eyeballs. Rather you need to build interaction and create a level of comfort"

Why do I blog this? not really a surprise IMO but since I am documenting failures for a project, I add this to my list of common problems. There would also be a lot to draw about the over-expectations that concerns 3D.