I think the concept of having a chatbox is unnecessary. I say this for a couple of reasons.
Firstly, we already have ways of communication in the Forum or outside. For example, we have topics to leave a comment on, Private Messages; Inbox, Skype, MSN, YouTube, dA and other things too.
Second, when I'm on the Forum, the only members online are me. Sometimes there may be some other users online, like 1 or 2 but they aren't using the Chatbox. They are using topics to comment in.
Lastly, the chatbox at the bottom of the page says 'You are disconnected', which tells me that I can't chat in that box. Likewise, it only shows up at the front page but if I wasn't disconnected, I'd like to have the Chatbox on every topic I go on. It'd be convenient too.
My suggestion is to not have a Chatbox if no one is around to use it.
Thanks for reading.