There was recently a really interesting conference held in San Franciso and another held in London on the very topic of sustainable IT - neither of them provided the means for remote participation for those of us who either couldn't afford to fly there or didn't want to pollute the atmosphere by travelling. This seems to be a classic oxymoron to me.
Conferences that charge their delegates should surely be able to provide such a service even if they charge remote attendees too. Even free conferences could take advantage of free services like ustream.tv
I will be pushing for any conferences (whether Green IT oriented or otherwise) that I'm involved with in future to stream their content.
Clearly it must be more complicated than it seems to me at this point to provide such a service - if you know of blockers and (ideally) ways around them then please comment on this post