In a recent Stress Test, the BigBlueButton community achieved over one hundred and sixty (160) simultaneous users in a session. The screen shot to the right shows a user viewing eight other webcams during the stress test.
You can see a full report of the stress test in this post to bigbluebutton-dev. (A PDF file showing bandwidth and CPU usage is available in the same post.)
This test was done using BigBlueButton 0.64.