I'm using Smoothwall Express 3.0 at home right now and it has major problems. I have an extremely basic setup and it keeps locking up (I have to hard reboot) when I am downloading a large file via torrent.
My setup is as follows:
[Road Runner] ---- [Smoothwall] ---- [Netgear GS108 (8-port Gigabit Switch)] ---- [Several other machines]
This is the most basic setup you can have and it's great when it works but it keeps failing (not gracefully at all) and it's bugging the hell out of me. I have tried tweaking a few settings to no avail. I will have to try something else.
Edit: I have fixed the problem. The NIC or drivers were bugging out so I replaced the NIC and used different drivers. That seems to have fixed the issue. With that said, I am not very impressed with the Smoothwall web interface. It doesn't work very well and is far from bullet proof. I'm sure there must be something better out there but I haven't tried anything else besides DD-WRT (on a router, not a PC) which was great compared to Smoothwall.