So, first of all – this one is the Good :)
I got this from the current print issue of weave magazine (a German interactive design magazine) where you can find an interesting article dealing with the forms of persuasive design. This is much about psychology and how to guide users to make (the right?) decisions.
I think this one is a great and inspiring example how to change peoples behaviour by making something more funny (and getting them perhaps onto a more better or healthy lifestyle)
‚66% more people than normal chose the stairs over the esculator‘