If you're the founder of a highly controversial forum owner, then it's best to keep it away from the spotlight. Of course, you do miss out on many potential members. The key is to then invite trusted friends over, and then encourage them to invite their friends, and so on.
No, I don't normally go hidden. As a staff member, I think it is important to stay visible so members can see when you are online so they can contact you and get a fast response. As I member, I don't normally go hidden but I don't see a problem with that.
I do every now and then, if I know there's a report waiting in the mod station and I'm waiting for another mod to help me with it, or if I just don't feel like being bugged at that moment of time, then I'll go hidden. I also tend to go hidden if I'm busy archiving threads or mass deleting/moving threads. 😛
Overall though, I don't like going invisible. I feel as if it takes away from the activity of the forum, since people will visit and see a few people online, when there's others online that aren't showing themselves. Ecspecially if you have a ton of people going invisible, it can easily eat up your forum.