tedster - 4:02 pm on Mar 20, 2010 (gmt 0)
Look at the faces in the audience. Are they "leaning forward" or falling asleep, checking their email, etc?
One of the biggest shifts for me over the past two years has been getting used to an audience where a large number are using Twitter. They may be doing it to share their appreciation for the talk, but the feeling of having a truly engaged audience is still not there, not the way it used to be.