80% of your spam appears to come from only 200 or so sources, many based in South Florida (the
Spam capital of the world). When the hurricanes hit last year there was a measurable drop in spam worldwide.
There's quite an interesting
article about what happens if you reply to spam. One in six were blatent scams, roughly the same fraction that turned out to be from people actually prepared to sell goods. However, just over half of their replies got no response, but just got the email address added to spam lists which were then sold on to other spammers.
These days my personal filter dumps pretty much everything not from the major US/UK top level domains (.uk, .com, .net, .org, etc.). Most of the stuff that gets dumped is US-spam, but with a faked email origin - at the moment I get plenty of spam that appears to come from Vanatu (!) which makes it quite easy to filter out. In the past I did some more filtering dumping everything with an extended character set (to get rid of all the Korean, Russian etc. spam that I couldn't read if I wanted to) but that seems to be filtered upstream these days.