I think offering control of the ActivPen is key to students being more engaged. If they aren't offered the opportunity to use the Promethean Board, they run the risk of being passive observers rather than participants. I was in a training once with a middle school teacher who had a SmartBoard and his philosophy was, the students should be touching the SmartBoard more than the teacher.
Today, students were manipulating shapes to demonstrate addition and subtraction of fractions. As a problem came up, one student was solving it on the Promethean Board, while others were doing it with manipulatives at their seats. Students at their seats were checking the student up front, while also checking their own work. The whole time they were staying on-task because they wanted to be the next one at the board. Very engaging.