My presentation this past Saturday at Podcamp Ohio was my first go at leading a session in an unconference format. If you're unfamiliar with the term "unconference", here's the wikipedia definition -

An unconference is a facilitated, face-to-face, and participant-driven conference centered around a theme or purpose.

As you can see, rather than serving as an "instructor" or "presenter," my role in an unconference is to be a facilitator. The idea is that "we" are smarter than "me" - that the aggregate knowledge of the group will provide far more value than the knowledge of an individual - in this case, me.
I tried hard to honor that concept, but taking a presentation developed using a traditional seminar model and turning it into a facilitated conversation was more difficult than I expected. It generally went well, but I walked away with a few lessons learned:

Have a Roadmap - While the intent is for the discussion leader to facilitate a conversation, the participants will get the most out of your session if you have a basic plan of what general themes or ideas are important to the topic at hand. That's not to say that you have to adhere slavishly to your plan (after all, sometimes you get the most out of unplanned side trips), but you should have one.

Listen More Than You Talk - Aside from your opening and closing remarks, the participants should do most of the talking. This may feel unnatural if you normally operate in the seminar/instructor mode but it's the heart of what an unconference is meant to be.

Turn The Projector Off - How can you prepare effective slides if you don't know what the participants are going to talk about? If you feel naked without a slide show, at least limit it to a few (emphasis on 'few' - no more than 2-3) introductory slides to establish your credentials and the session topic.

Pick Up A Marker - Use a whiteboard or flip chart to record the key points of your session. Ask someone to be a scribe if you're not good at simultaneously leading a discussion and writing.

The Participants are the Experts - Even if they're not. In  an unconference everyone's ideas and opinions are welcome. Your job as facilitator is to lead the participants in discussing the validity of those ideas and opinions.

In my presentation Saturday I'd say I batted about 50% at honoring those points; the hardest for me as a traditional speaker being the "listen more than you talk" precept. I enjoyed the experience, though, and have become a believer in the effectiveness of the unconference format. And, since practice makes perfect, I'll be looking for more opportunities to facilitate unconference sessions.