Infection notification by ISPs
I'm all for greater ISP involvement in fixing this. Treat a botnet like a real world epidemic and quarantine the PCs until they fix the problem. Only allow email in and access to ISP webpages showing how to clear the problem. Use the customer postcode to provide a list of computer experts in the area they can pay to sort it out.
ISPs are doing deep packet inspection anyway these days, so rather than wasting time looking for pirated software or music, actually make use of the info and look for botnet behaviour. Must be something they can search for even if it's just an unusually high email burst.
Plusnet have their own broadband firewall you can turn on which only allows common ports to be used and is fairly fine grained. Much as I don't like opt-out, perhaps that should be the default so power users can turn it off.
Yes, people will just get re-infected a week later if they are stupid. But once they keep getting cut off maybe they'll think twice next time. I'd choose an ISP if it advertised that it quickly cuts off infected PCs.
I seldom see junk mail these days, and yet there is apparently tonnes of it about. So ISPs are stopping most of it for us. It's in their interest to kill of the spam-spewing PCs, either their own or to inform other ISPs and get them to do it.