At my workplace we get approx 16000 spam that hit our firewall per day but they are all blocked except for a few stragglers by our excellent perimeter security. I get maybe 2 a day after filtering which is pretty damn impressive.
Admins, I've run forums before and the only way to beat the spambots is to have admin activated accounts only after a reply email is received. A bit of extra work but it is 100% effective.
