Would it be possible for the Shoutbox to appear on the forums when you aren't logged in, or haven't created an account yet? Being able to do so may encourage more signs ups since the guests can jump into immediate discussion, or can just "hang out" with the members right away.
Before joining ZD, I was out of the forum game for awhile, and it was a very pleasant surprise seeing that a forum could have a shoutbox/chat room.
Of course, if the unregistered guest tries to post in the shoutbox, a prompt could come up and say "Thanks for participating in our Shoutbox! In order for you to chat, you'll need to create an account! Click here to register."
Edit: Also, is there a way we could add fun facts and interesting links for unregistered guests? When you visit the forums as a guest, its just the regular forums with no shoutbox. If we had a paragraph on top of the web page that encouraged them to sign up, and let them know what fun things we do here (like shoutbox, competitions, awards), they would be more inclined to sign up and get our activity up.