When I entered the Willis building (Aug 8) to get to the sky deck they told me the wait was a 1,5-2 hours! It did put me off a little, but it is peak season so I didn´t know what to expect. I had my "1Q84" book by Murakami with me so I came a little prepared..
They were right, it was 2 hours later before I reached the top!
But then I will never get this exact view again, so I will say it was worth it!
Walking on air!! It was a bit creepy, I couldn´t help but fear that the glass construction would break!