I was invited to Foo Camp (which is now being blogged just about everywhere) but sadly couldn't go because of finances this year. I would have enjoyed it I'm sure.
Some people sat down to try and discuss ways to solve the spam problem.
What Tim misses in the above idea is that machines are being hijacked en-mass to send spam. It's only a small step for the spammer to be able to hijack machines that have paid to send email. Thus his fictional SMTP4All Inc now has major lawsuits on its hands from innocent victims who have been overcharged.
This is just another in a long series of reasons why sender pays is just another short term stop gap solution.
If you really want to solve the spam problem I think you have to break a lot more eggs than is being proposed here. And I'm not convinced that's a price worth paying.