Personally I would really like some transparent filtering features, I
understand m0n0wall is meant to be firewall but why not make some kind
of "m0n0wall plugin" features where you can add programs like ClamAV,
SNORT or Spamassassin if you have a more powerfull machine? I know
there is an alternative called Pfsense which looks to be very
promising, but on my machine it wasn't exactly stable. I'll test that
software as soon as there is a stable release.

At the moment I have decided to run Astaro since this is the only
software capable of acting as a filtering bridge while having
transparent antispam, antivirus and intrusion detection running.
Allthough I will have to buy a license it will save me a lot of time.

If I ever need "just a firewall" I'll definately consider m0n0wall
again, so far it has been one of the easiest and most stable
opensource firewalls I have tested :)