Billboards work because it's captive traffic. Very few if any sites on the net have captive traffic. Twitter certainly doesn't even in the current model and I t

Billboards work because it's captive traffic. Very few if any sites on the net have captive traffic. Twitter certainly doesn't even in the current model and I think the model you're describing would be even harder to manage in terms of spam and abuse, not to mention coordinating with law enforcement. So likely even less captive.