I was just imagining today the idea of people in the classroom, with notebook computers or cell phones or whatnot, being able to raise red flags anonymously when they aren't following. The number of red flags from different students could control a general classroom "temperature" visible on your own projected screen.
If the temperature gets too high, it's time to slow down. Also could allow full anonymous questions to be sent up.
The goal here being to let people give anonymous feedback if they are afraid of looking like dummies in front of the crowd.
Could be cool, or maybe old-fashioned watching faces and asking for questions is better.