FWIW, this is my .procmail script running on the MetaArray. It does a decent job of filtering out alot of spam. 

-------

PATH=/usr/pkg/bin:/usr/local/bin:/usr/bin:/bin
SPAM=$HOME/mail/Spam
LOGFILE=$HOME/procmail.log

SENDERIP = `formail -c -XReceived | grep "by sdf.lonestar.org" | \
grep -v "from sdf.lonestar.org" | \
sed "s/^Received: from .*\[\([0-9]*\.[0-9]*\.[0-9]*\.[0-9]*\)\].*by sdf.lonestar.org.*$/\1/"`

:0
* SENDERIP ?? ^^[0-9]*\.[0-9]*\.[0-9]*\.[0-9]*^^
{
        SENDER_REVERSED = `expr "$SENDERIP" | \
        sed "s/\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\)\.\([0-9]*\)/\4.\3.\2.\1/"`

        KNOWNOFFENDER = `host "$SENDER_REVERSED".zen.spamhaus.org | \
        sed "s/^.*\(127\.0\.0\.[0-9]*\)$/\1/"`
        :0
        * KNOWNOFFENDER ?? ^^127.0.0.[0-9]*^^
        {
          :0 fhw
          | formail -A "X-Suspected-Spam: RBL - BLOCKED - zen.spamhaus.org"

          :0:
          $SPAM
        }
}

:0
* ! ? if [ -n SENDERIP ]; then rblcheck -q -s dnsbl.sorbs.net $SENDERIP; fi
{
:0 fhw
| formail -A "X-Suspected-Spam: RBL - BLOCKED - dnsbl.sorbs.net"

:0:
$SPAM
}

:0
* ! ? if [ -n SENDERIP ]; then rblcheck -q -s or.orbl.org $SENDERIP; fi
{
:0 fhw
| formail -A "X-Suspected-Spam: RBL - BLOCKED - or.orbl.org"

:0:
$SPAM
}

:0
* ! ? if [ -n SENDERIP ]; then rblcheck -q -s relays.orbl.org $SENDERIP; fi
{
:0 fhw
| formail -A "X-Suspected-Spam: RBL - BLOCKED - relays.orbl.org"

:0:
$SPAM
}