It seems like we're reaching some sort of critical mass for mixed-reality events. Within one week there are/have been:
USC's Center for Public Diplomacy's Awards Ceremony, which was attended by more folks in Second Life than in the real world. 3 out of the 4 finalists were created within SL. The very polished Peacemaker won, but Hydro Hijinks made it a tough decision.
The Berkman Center's Beyond Broadcast conference is happening right now. Focused on the future of public media, it has been very interesting watching virtual worlds recognized as legitimate option.
This weekend will see BBC Radio 1's One Big Weekend within SL. Two days of free, great music and now you don't have to get to Dundee to enjoy it!
Of course, the real questions all resolve around how valuable these mixed reality events are when compared to a web cast. The mixed reality event allows remote participants to also connect with each other but at the cost of more technical requirements and bandwidth. The ultimate success of these events will be determined by whether that tradeoff is worth it. I was smiling during the USC event because there were a ton of side discussions going on in the SL audience. It reminded me of being in the back row of a session and making comments or jokes with other folks sitting nearby. Audience chatter can become loud enough to constitute real-world griefing yet it can be among the most important and enjoyable parts of attending. I've had more than one long-term friendship instigated by a joke or flippant remark made during a talk. I suspect that the same will become true in mixed reality events, where it's the unplanned interactions of the audience that lead to new social connections and fun.