Which communities do you find yourself most actively participating in? What makes them compelling?
Are you part of any online groups that have regular offline meetings? How do the two intersect?
Describe someone you met on LJ who's become a close friend, and how your online and offline communication developed.
Describe some unusual, creative way you use LJ or have seen it used.
What questions do you think audience members might have? What do you think we might be able to tell them that they hadn't known about before?
Talk about anything else you think is relevant!
(My own answers will appear in the comments.)
Oh, and please use photographic userpics if you have them, so that we can all recognize one another when we get to the room. *grin*