Some online communities introduced virtual currencies in order to have users strive for a higher rank, value, or in whatever the currency might exist. An online community can be any connection of users from discussion boards, social networks or a user group.
Online currencies can change the way users behave, especially when they are tradable against real money. Depending on the general topic of the community, the users might even be adverse against any form of gamification, while other audiences applaud even the slightest gamification forms.
The article “How to Introduce Virtual Currency into your Community the Right Way” describes just what it says.