I wrote a small script to give me a count of users spam and ham. It's terribly inefficient, but got the job done:

set lastname=""; set count=1; for name in `grep "identified spam" /var/log/maillog* | sed -e "s/.* identified spam .* for \(.*\):.*/\1/" | sort -u`; do nonspam=`grep "clean message" /var/log/maillog* | grep $name | wc -l`; spam=`grep "identified spam" /var/log/maillog* | grep $name | wc -l`; ratio=`perl -e "print $spam/$nonspam"`; echo $name: $spam spam, $nonspam non-spam, $ratio; done

Produces output like this:

ed: 1341 spam, 144 non-spam, 9.3125
fred: 3276 spam, 948 non-spam, 3.45569620253165
ned: 797 spam, 32 non-spam, 24.90625
jed: 3411 spam, 2433 non-spam, 1.4019728729963
sed: 657 spam, 248 non-spam, 2.6491935483871
bed: 204 spam, 17 non-spam, 12
bled: 3701 spam, 233 non-spam, 15.8841201716738
med: 173 spam, 162 non-spam, 1.0679012345679
ved: 159 spam, 129 non-spam, 1.23255813953488
zed: 1785 spam, 328 non-spam, 5.44207317073171
  ¶ 4:21 PM