I patched it so that "Invisible" is no longer displayed (after tonight's update).

I checked out other forums with similar "Magic Magnum was last seen 2 hours ago" UI (like Xenforo) and they just hide your online-now icon and your last-seen-at timestamp. Of course, like on the Guild, you know if someone has invisible-mode enabled because they have no last-seen-at timestamp.

My reasoning for showing "Invisible" to begin with was that it possibly made the UI more obvious/consistent. i.e. "Why can't I see this one user's last-online-at timestamp?". But yeah, it's not something that needs to be broadcast with every post. 

Aside: Invisible users will no longer show up in the "Who's Online" list after tonight's update. That was definitely a bug. The invisible-mode toggle will also appear on the edit-user page as well after the update.

Thanks for the feedback!