Brant and Jonathan covered it very well. A faster shutter speed would have most likely helped. A tripod would have helped as well.

The lens you have can take very sharp pictures. You will have several advantages with more expensive glass. One will be a wider aperture will allow you to have a faster shutter speed. It keeps you shooting longer as evening rolls in as well. Another will be resolution, the big white lenses are much sharper, but you shouldn't notice this very much on your computer screen looking at it at its normal size. It is when you start to zoom in to the picture and pixel peep and crop that you will see it. This is a stick and stone way of judging but the way I judge the sharpness of an individual picture is when I am reviewing with adobe bridge I zoom in. 100x 200x 300x and so on. The difference I found between the 100-400mm and say my 500mm is that I could zoom to 100x sometimes 200x with the 100-400 but could go quite often to 300x and 400x with the 500mm. So with the big white lenses they will allow you to crop your image more than you will be able to with your 100-400.

So speed and cropping are two of the benefits. But you should still be able to get sharp pictures out of your 100-400.