I suggest you customize one or more of the view’s tools.
For example, if you just want to save/restore your information when the user does a drag (i.e. a move or a copy of the Selection), define your own tool inheriting from GoToolDragging. Override the Start and Stop methods – be sure to call the base methods too.
You’ll notice, for example, that a number of example tools in the sample applications do this to change the Cursor or create and cleanup other side-effects.
You can also override the GoTool.DoMouseMove method, to get called frequently during the mouse move.