Interesting piece by TechWeb News on Microsoft employee Raymond Chen, who has "saved every spam message and virus-laden e-mail he's received at work since 1997". More intriguingly, he has "graphed the spams and viruses to create a cool visual representation of one man's malicious traffic".
The resulting chart is fascinating. You can see the whole Spam Phenomenon in blue and red, especially as it went 'ballistic starting in 2002'. Worth reading for the comments alone. Clearly there are a lot of spam historians out there.