We proposed a reputation mechanism for mash-ups/apps that can be plugged on OAuth. The service provider (e.g: Twitter or Facebook) records every access to the user account and sends a report after a week. Users rate the application which reputation is maintained by the service provider. Average ratings and comments are displayed when a new user is asked to grant an authorization.
Link to the paper: http://www.dundal.com/R2M-CCNC2010.pdf