Where did all the spam go?

I used to get over 400 spam email messages a day, say a year ago.  In the past 14 hours I got only 38.  It seems like recently I get barely 100 spam emails a day.  What's going on?  Are the spammers on summer break?  Or could it really be that people are doing a cost benefit analysis and simply deciding that the return on investment for spam is starting to suck?  Is Microsoft putting pressure on these guys?  Anybody have a clue as to what's going on?

For reference, I am not using any anti-spam software and not even using any email filters.  Virtually all of my email comes through non-ISP web servers.  And, all of my web sites and blogs explicitly list my email address.

This seems too good to be true.  We'll have to see how spam traffic shapes up after Labor Day in September.

-- Jack Krupansky