I read a great analysis of Foursquare badges that users actually earn a few months ago, and unfortunately I can't find it again. The gist, though, was that almost all users get the badge for visiting one place, a few less get 5 places, etc. and very few peole get the badge for visiting 50 unique places. On the other hand, the badge for visiting the same place a whole lot was much more common. The conclusion was that the badges might reinforce things users were inclined to do anywaybadges might reinforce things users were inclined to do anyway (visit their favorite place a lot, which they argue is more common), but they weren't enough to change behavior to something elsebut they weren't enough to change behavior to something else (try something new every night).
The same might not hold true for something like the Nike run tracker thing, or other things where the user is intrinsically motivated to change their behavior.
