The iPad is much less intrusive in collaborative contexts than either a laptop, which tends to come between members of the group, or an iPhone, which isolates individuals, severing each from the dynamics of the whole.
Chris nails it IMO with this statement about the iPad. I tried to articulate that in the Chronicle piece that came out yesterday but didn't say it quite as well. What I have noticed over the last week is this thing changes both my own in meeting behavior and the perceptions of my attention. I tend to lay it flat, flip it on and off as needed, keeping it from standing between myself and the rest of the room. Doing this tends to keep my eyes up more and (I think) more fully engaged.
If the iPad can alter the dynamics in a meeting what can it do in the classroom? Until these types of devices become more widely adopted we can only wait and I am not quite sure we can generalize classroom dynamics from the way we view them in our administrative patterns of interaction.