I use FreeBSD 5.2.1 + pf/altq (Score 1)

For those that don't want to migrate to OpenBSD FreeBSD 5.2.1 has support for OpenBSD's pf and altq via a port, although you need to patch your source tree by hand. FreeBSD 5-current has fully integrated support for pf and altq, although I would wait for FreeBSD 5.3-RELEASE, rather than trying to use current. I personally found ipfw and the queueing subsystem extremely hard to use. That said, FreeBSD 5.2.1 on my k6-233 works great for our LAN. I use it to prioritize dns/www/smtp/pop3/imap, put leechers into their own bandwith limited queue, and set aside ~4kb/s upload for priority stuff. It has had an amazing effect - lag is completely gone, and leechers don't affect the latency of the LAN's connection anymore.