eWeek has an editorial about the recent surge of spam:
Everybody's seen it by now. Spam is up like gangbusters in the last few months. And not just in volume; a lot more of it is getting through filtering mechanisms that had previously been pretty reliable. It's an aggravating and depressing situation.
A number of factors have contributed to the situation, and what they all have in common, unfortunately, is that spammers are getting much more sophisticated.