As far as free firewalls go, I think ZoneAlarm (basic) is alright, but not great because of it's very limited set of features (program controls, limited ability to change settings, VBS e-mail protection only, and basic port blocking).

It sounds like Kerio is pretty robust as far as features on a free firewall. I'll have to check it out for some friends and family's computers.

For those using Smoothwall and BlackICE, how do they compare?

As for myself, I run ZoneAlarm Pro because I really like it's features (Pop-up blocking, cookie control, password protection to keep people from turning it off, e-mail virus protection, cache cleaner, etc) and have found it to be very reliable.