The Andrew Sullivan of Email
Everyone I know complains that they can't keep up with their email and that responding to it takes too much time. And of course, this is the same justification a lot of people use for either not starting a weblog or for abandoning one.
However, lots of bloggers have found it's worth their while to update their sites if they put out a tip jar or PayPal link and get donations from their readers to subsidize the time they spend writing.
So 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.")
It's micropayment mania!