I think I'm about ready to start running my SMTP proxy/filter for people now. I've got two users setup and it seems to be holding up just fine. I've managed to remove the need to manually create things, so I'm capable of adding new domains on the fly.
For my personal mail handling yesterday was the first day I've received over 10,000 messages. These are the stats from yesterday showing what happens at SMTP-time:
Total Mails : 13302 Total SPAM : 12620 (bounced back) Total Accepted : 682 Spam Percentage: 94.87%
So I've dropped 95% of incoming mail at SMTP time, which is a big win. Of the mail which was actually delivered I'd guess that pyzor, razor, and spambayes marked a further 50% of it as spam.
So my proxy needs to do better ... but it's pretty impressive.
TODO: Find people to run as guinea pigs, register a domain, profit.