Grum has been demolished, Lethic harmed
I've never considered spam to be one of the greatest problems. Even when my primary e-mail account belonged to the domain of a countryside university that just didn't have resources to protect the HEP physics users against spam – I think it was called the Harvard University – I was getting something like 30 spam e-mails a day and the peak was short.
When spam was born... This 1970 Monty Python sketch (filmed before Al Gore invented the Internet) is the actual reason why e-mail spam is called spam. The similarity was recognized and the term spam was coined by trolls who spammed early Internet forums by many copies of the word "spam". :-)
With an efficient enough mail client where I could simply press "D" 30 times, the problem was equivalent to losing 30 seconds a day.
Gmail and other major providers have sophisticated methods to filter spam. I could still observe something like 1,000 mails redirected to the spam folder each month. The filtering worked very well, perhaps too well; a more problematic issue were the rare problems in which a non-spam mail was classified as spam but I think that I have already setup the white lists to avoid such things. What about you?
Recently, the spam folder would only contain 800 e-mails or so. Chances are that in a month, it will only have 400. What about your numbers?
The reason for the expected drop was that the third major botnet called Grum was demolished:
The network was sending 15-30 percent of spam mail every day: almost 20 billion mails a day means that if you're an average user, you got several if not a dozen of spam emails from this botnet every day. Another botnet, Lethic, was scared so its "production" decreased, too. In combination, the spam rate may have decreased by 50% from Monday. Quite a change in several days. Of course, one could ask why it wasn't done earlier.
I think that spam is one of the problems that isn't really a difficult problem for the civilization. There are many other examples, too...