I have a Unix shell account for my primary email, and I run SpamAssassin on it. Very few false positives or false negatives, with the threshold set to 4 points, and the delete-it-outright threshold set to 10 points. I'm considering dropping the delete-it threshold down a bit, since it seems to be so reliable.

Here's what it gave me for a recent spam:

Content analysis details:   (7.40 points, 4 required)
FROM_ENDS_IN_NUMS  (0.7 points)  From: ends in numbers
EXCUSE_1           (0.7 points)  BODY: Gives a lame excuse about why you were sent this spam
HTML_WEB_BUGS      (0.1 points)  BODY: Image tag with an ID code to identify you
HTML_TAG_BALANCE_TABLE (0.2 points)  BODY: HTML is missing "table" close tags
HTML_50_60         (0.5 points)  BODY: Message is 50% to 60% HTML
HTML_MESSAGE       (0.1 points)  BODY: HTML included in message
HTML_IMAGE_ONLY_06 (1.1 points)  BODY: HTML has images with 400-600 bytes of words
DCC_CHECK          (3.0 points)  Listed in DCC, see http://rhyolite.com/anti-spam/dcc/
RCVD_IN_SBL        (1.0 points)  RBL: Received via SBLed relay, see http://www.spamhaus.org/sbl/
                   [RBL check: found 121.4.60.69.sbl.spamhaus.org.]