I'd like something quasi-official if possible, so I can tell my bosses: according to this report, even with diligent spam filtering, xx% of the email people receive is still spam. If fewer than xx% of your email is spam, we're ahead of the curve.
I only filter mail for myself, and I'm aggressive in scoring. I get around 100 spams a day, about twice that in a few mailing lists (including this one), and anywhere from 0 to maybe 10 personal messages a day.
I can't remember the last time I saw a spam make it into my inbox, but a little digging indicates that it was on 8/19. There was another on 8/5, and then some back in June.
So it looks like I get one spam leaking through on the order of every 10K spams sent.
Loren