What if there were a database of commercial email senders which published a score (like a credit score) that was based on how well they complied with best practices?

Return Path launched just that last week and its called the Sender Score Reputation Monitor. It's a reputation service for commercial mailers. Return Path is collecting over 60 data points on over 50 million mailboxes. Data points include unsubscribe compliance, complaint rates, unkown user rates, security practices, and identity stability.