I'm in rather a new position: I've actually gotten a colleague
enthused about TDD, and even NMock! He's an engineer, w/o much
experience writing GUIs, and now he's looking to me for advice about
the MVP pattern.

So much for the preamble. We have a requirement for (relatively
simple) drag-and-drop, simply from one control on the app to another.
How should I think of this in the context of MVP? As you may remember,
the control from which an item is dragged has to handle the ItemDrag
event, and the target control has to handle DragDrop. Now, I could
certainly have the presenter provide the object passed to DoDragDrop()
by the source, and the same or another presenter actually deal with
it, once the handler for DragDrop has pulled it out of
DragEventArgs.GetData(). Is this a case where, as with data binding, I
basically entrust the mechanics to .NET, and simply verify the results?