From Wednesday's Globe and Mail (Social Studies):

Every day, 10 billion spam e-mails are sent, reports The London Observer. This number is expected to grow to 30 billion a day by 2005.
Furthermore:
There is 25 times more spam now than at the start of 2002.
One in 12 British e-mails is spam. In the United States, spam now accounts for 37 per cent of all e-mail.
In a recent experiment, it took just 540 seconds for a new e-mail account to receive its first spam.
Up to 90 per cent of all junk mail is sent by 150 spammers.