Spam
While this isn't an official total since I only started tracking manually filtered spam since Feb of 2005 the averages are still pretty horrible. The totals for 2005 are as follows:
83K messages were delivered to me in 2005
Spam Assassin (SA) helped automatically flag 50K as spam (60%)
I manually flagged 17K as spam (20%)
This means that 80% of the email delivered to me was spam. YUCK!
I've been toying with the idea of using a whitelist only system to receive mail. The problem with that is then random people can't send me email and I've gotten some random email that I would want to get. If you then add on some kind of autoresponse with manual authenticate then those people could send you email, but I'm sure most wouldn't. In researching solutions since my hit rate for SA was so low I stumbled upon the simple idea of "why not use multiple different filters".
If spam can be constructed to defeat a certain class of program its likelihood of also being able to defeat other programs is not as good. The simple extraction from this then is that if you use multiple programs and use a combined weighted score to determine if a piece of email is spam or not you are much more likely to find spam and much less likely to have false positives.
Implementing and maintaining such an approach is much harder, but the idea is that once you have it setup you should be able to easily maintain it. I just need to find some free time to sit down and do that.