It's probably the one most used gamification/persuasion element across all kinds of UIs, especially apps. But in most cases it is tied to a social leaderboard of some sorts.
I've been reading this series of gamification articles and the author often uses World of Warcraft for comparisons, where community is a crucial factor. I know we humans are social creatures, but I'm wondering if this has to be tied to social systems.
Does anyone here have some form of "proof" that it works in a single user setting too? (e.g. an app for exercise or halthy eating)