Bear in mind that using the CP on a wide angle shot may cause a gradation in the color of the sky from one side to the next. The CP is most effective at 90 degrees to the sun. In a wide angle shot, the angle with the sun shifts significantly across the field of view. Therefore, the effectiveness of the CP changes. You may have one side a nice, deep shade of blue and the other side a noticeably paler blue. I was reminded of this recently when I had a day at Lake Tahoe. The CP was beautifully effective in reducing the reflections on the surface of the lake and made the rocks beneath the surface visible. However, some shots had a very noticeable shift in the shade of the sky from one side to the other.
Another interesting phenomenon was the reflections of clouds on the surface of the lake. They were very visible but not just a simple selection; it was more like a beam across the surface of the lake, like you might get from the sun or the moon.
That being said, I soon thereafter bought the lens that I wish I would have had with me on the trip: the Tokina 11-16 DX AT-X Pro. That would have made some nice sharp landscape shots for me (that is, if my lack of talent would permit!).