Here's a silly idea: let's try adding an option for hashcash to APEX. (Or has someone already done that?)
If the problem with hashcash is that worms can steal CPU cycles to generate hashcash, then let's attack the problem of worms separately from the problem of spam suppression. If the problem with hashcash is that poor people are taxed more heavily than rich people for the utility of spam suppression, then-- well-- they should upgrade their CPU's, now shouldn't they?
And as for those too poor to keep their CPU's current, Let Them Eat SMTP. They clearly have an unhealthy interest in paying to receive MAKE MONEY FAST spam, so we should encourage them to continue using SMTP anyway. The Internet interprets censorship as damage and routes around it. Let SMTP continue to serve the useful function it serves: carrying spam messages.
-- j h woodyatt <jhw@wetware.com>