I'm counting the spam and ads as well, because they take the same amount of time as if they were paper junk mail coming into my actual mailbox. It's only a couple of seconds, but it does add up.
For the month of April, I received 890 e-mails on my work account. This comes out to 40.5 for every work day.
I think I'll start doing the same thing with my personal e-mail as well -- just to see what I find out.