http://planetnexuiz.com/ladder/?p=Rules
Personally, I think that a weapon should do damage if it hits someone, regardless of whether they are an enemy or not. If you have a problem where you are killing your teammates or they are killing you a lot, then that is a problem with weapons tactics. You should just be more careful about how and when you fire your weapon. If your teammate is in front of you...don't shoot

I understand the complaint in that it allows an enemy player to rush into a base and cause more havoc than if there were no friendly fire. It makes defense harder. But I think that's just a reality that should be accepted and should be taken into consideration with strategy.
I've been working with a compromise of a setting of either 0.3 or 0.5. I've mostly been using 0.5, which means that your weapons do 50% damage toward your teammates.
I'm not trying to simply emulate ladder rules. I want to find something that will make most players satisfied. I want to know what you guys think is ideal.