My nun-chuck was so sensitive that sometimes when I was running around, I would move my hand up to brush hair away from my eyes and Link would pull out his shield. During the bug-catching game near the end I actually had to un-equip my shield because whenever I went to catch a bug, I would trigger the nun-chuck sensors and it wasted precious time. While I really like the feeling that you were actually holding your shield out and that there was a specific motion for it, I do agree that I think while they focused a LOT on the sword during the production of the game that the shield was not quite at planned out.
Although it was still pretty cool, I had more qualms with it than the sword. But alas, not everything can be perfect... it was VERY close to being so, though! ^^