Facilitating in the dark

I'm a huge fan of distributed, & open ways of working, but it is not without its challenges. Monitoring the vibe when facilitating a workshop via video conferencing is particularly tricky.
In person, we can easily read people's body language. Those who are not speaking are still contributing their time, their attention and their energy. We can easily see if people have become bored, or are distracted. Online it's hard to sense if lurkers are learning, listening, thinking, multi-tasking, or just completely tuned out.