This screenshot was provided by MICA - the Meta Institute for Computational Astrophysics, a scientific group of professional researchers that only exists inside virtual environments.
The image is of a MICA conference, held in mid 2009, in the VR environment Second Life. It clearly shows the problem with such organisations in worlds such as SL. The sparce scattering of avatars represents less than a quarter of MICA's membership at the time. It also represents al lthe avatars the sim environment could support.
Until this issue is addressed, large scale events in VR, are simply not feasible.
Link: VR and Conferences: The Difficult Partnership
Link: VR for Research: Not the Medium, but Delivering the Message