SpamUnit has two excellent articles on the history of spam and present trends. From an end user's perspective, an average email address attracts 400 spam e-mails a day.
Sophos states that "Only one in 28 emails legitimate".
Spam contents, delivery and statistics are tracked and updated in near real-time by Marshal and Barracuda. See Barracuda's report on Worldwide email threat activity and Marshal's Spam Statistics.
Here's Marshal's chart on various types of Spam, as of August 2008.
And dont miss Spamhaus's reports on the worst networks, spammers and countries are below, updated monthly.
The 10 worst spam service ISPs.
The 10 worst spammers.
The 10 worst spam origin countries.
Terry Zink's Anti Spam Blog features excellent information and research and is up to date with the latest trends. His article on "How much do spammers actually make" breaks down the expenses and income for an average spam week:
|Spam Sent||40 million|
|Click through ratio||0.12%|
|Total sales revenue||$37,440.00|
|Spammer Commission rate||50% (Gah!)|
|Total spammer income||$18,720.00|
|4 days of botnet access||$6800|
A net profit of $7690 per week sounds very lucrative!