Earlier this year I used to track the number of messages I'd send. On a busy day it'd be 150, on a slow day 75. It's much less than that now I'm head-down bum-up in the PHP book and letting email stack up.
I ran some scripts over my archived outgoing mail and came up with a total of 15,673 messages sent in 2001. That's about 40 per day on average, no allowance for weekends, holidays, etc. I guess not every day is a busy day now:-)