It appears that Tom Beecher via NANOG <nanog@lists.nanog.org> said:
Barry has a reasonable theory - that the economics of spamming is brittle - but it is just that: a theory.
Part of the theory itself is generally sound. If spamming isn't making someone money, much less spam would be sent.
However, the assertion that the spam economy is 'fragile' doesn't really hold up. The number of spam emails hasn't substantively decreased in a long time. Year over year, it's generally flat to increasing. ...
I'm still seeing 90% spam but many people I know say that it's dropped to more like 50%. My guess is that the spammers have just figured out how to do it a little more efficiently. 50% is still awful. T's, John PS: my system is small and strange and has a lot of honeypots so I'm not surprised spammers keep trying.