you can't manufacture community
John Allsopp has a great post on the ebb and flow of true community (and creativity): dog or higher: harnessing creative anarchy - an abject lesson.
No matter how much companies are willing to pay for community sites like Flickr and LiveJournal, you cannot buy, bottle or manufacture the creativity of the original user group. Communities have a shared energy, a sort of consensual X factor. When it is strong, great things can happen; particularly when the group governs itself and the members feel content. Impose someone else's rules on a community and that energy usually leaks away, seemingly overnight.
Even the simple act of buying a community like Flickr can be the ripple which triggers the end. Even if the entire community is operating the same way and the only difference is the knowledge that someone different owns it. Collective consciousness is a hard beast to predict.
Sure, communities can continue on well after such a moment. They may never recapture that original spark, but sometimes new and wonderful flames develop in its place. Other times, it's just tradition or a diluted experience which lasts beyond the departure of the original soul. Some communities have a great will to live and a more developed ability to reinvent themselves.
Perhaps the thing to realise is that a functioning community (or creative outlet) may fall apart if you interfere with it. So don't meddle unless there is a compelling reason to do so.