I'm sure that you occassionally get real mail tagged as spam in SA.

To fight this I go through my spam box by hand, which is annoying.  To 
help, I've figured out how to put the spam score in the subject, so you can 
get a huerestic about how spammy the email is.
The line is:
rewrite_header Subject [_SCORE_]and that goes in your spamassassin user_prefs (~/.spamassassin/user_prefs).
Your spam should come out looking like this:

Subject: [11.7] Public Relations Conference for Nonprofits

This is nice because you can sort your spam directory by subject, and 
instantly find all the "near miss" spam.