I like it – cost spammers some money if you don’t like what they’re selling. The model is nice, can be applied to any sort of contact – you attach a ‘bounty’ to your mail, and if the recipient feels you’re wasting their time then they can claim the bounty, else they leave it. If you don’t trust your audience, you’d give a small bounty if they might claim it, but then as a recipient I see that you think I might take your bounty so I might choose to ignore your mail. You’d have to get it right to make money…spam squashed.