Two of the BigBlueButton developers, Richard Alam and Fred Dixon, gave a talk at SC2011 - Software Developers' Haven, an open source conference held in Ottawa, Ontario, on August 27, 2011.
They presented the architecture and implementation of record and playback in the upcoming BigBlueButton 0.8.
At the time of the presentation BigBlueButton 0.8-beta had not yet shipped, but it will soon!