Anil Dash has an interesting idea:
why not have a message at the bottom of your outgoing email messages
telling the recipient how much you're willing to bid for a timely
response to the message? (“If you get me an answer on this in 8 hours,
I'll PayPal you a dollar. 24 hours is worth 50 cents, and I'll give you
a quarter for a reply any time in the next three days.”)
Make it an X-header in the email so my email client can read it and I can sort/prioritize by the “bounty” offered by the sender.