It looks like “sold out” might be the next way to determine success for a viral marketing campaign. This is as reported by WOMMA, but it’s been picked up elsewhere over the weekend:
The response to Paramount’s “Indiana Jones” Facebook campaign has been enormous — with all of the 250,000 available Indy-branded Fedora free virtual gifts being snapped up and sent to friends in under 12 hours.

Of course, if they had decided to offer 1 million virtual fedoras on Facebook, that would just cause a glut in the market.