The iMoot team have been using BigBlueButton since 2013 to help facilitate a biannual online learning event focusing on Moodle - the iMoot. The event runs runs across timezones and has a global audience of hundreds.
Without this awesome open source web lecturing and web conferencing system, we would not be able to run our event. Fred and the team at Blindside Networks are so responsive to communication, and have gone out of their way to help and support us.
I thoroughly recommend BigBlueButton to anyone looking for a reliable and scalable web conferencing system designed for online learning.