Hey, my Engineering Maths lecturer has a touch screen laptop type device (I don't know any more details sorry) which he plugs into the projector and he has an instant interactive whiteboard. From what I've seen from it so far it's great, can teach to a whole lecture theater of nearing 300 students. As an added benefit, the lecturer can look up and tell us what he's doing instead of turning around, he therefore doesn't hafto turn away from us students at all. Moving from the interactive board to powerpoint slides is no problem either, the transition does look very professional. We had Activboards in my old school though and they also presented no problems apart from the whole turning around thing.
Hope it helps.