Like my graph of Usenet posts, I've graphed the amount of email I've sent over the past ten years.
What surprises me is how steady the email stream is. There's a gap for a vacations I took summer of 1996 and spring 2001. And a drop-off after I started working at Google in 2002 (I'm not indexing my Google email). But basically my email sent has been roughly the same for the last ten years. Weird.