Here's a script that can be pasted into a shortcut key, preselect 2 planar faces before running it. It will report the angle between the plane normals.

script: var faces = moi.geometryDatabase.getSelectedObjects().getFaces();
if ( faces.length == 2 && faces.item(0).isPlanar && faces.item(1).isPlanar )
{
	var A = faces.item(0);
	var B = faces.item(1);
	nA = A.planarFrame.zaxis;
	nB = B.planarFrame.zaxis;

	var dot = (nA.x * nB.x) + (nA.y * nB.y) + (nA.z * nB.z);
	var angle_radians = Math.acos( dot );
	var angle_degrees = angle_radians * 180.0 / Math.PI;

	moi.ui.alert( moi.ui.formatNumber(angle_degrees) );
}
else
{
	moi.ui.alert( 'error - 2 planes not selected' );
}

- Michael