It depends on the forum, really. Most of the communities I’m involved in are informal, so there’s no need to be officious or super strict. I don’t think there needs to be that separation between staff and members in a community like that. Yes, there are times when that distinction needs to be made and discipline needs to be doled out, or situations need to be calmed down, but I think it’s important for staff to be relaxed and informal. It’s more encouraging for members to interact if they don’t feel like they’re at risk of being punished for this, that and the next just because they get a little joke in here or there. Professionalism is nice, but you can mix professionalism with fun.
There are other forums, though, where a professional attitude is necessary. Those tend to be forums related to companies, products, and so forth, so it’s expected, but when it’s your forum, even if it’s a forum that generates income and serves as your livelihood, there’s room there for leniency and levity.