[ericw]

I have to disagree with the other two. I think the composition is great. If you left "space to move into" I'd bet this photo wouldn't feel nearly as fast. If he's on the left I'd look at the picture and say "hm.. he's got a lot of ground to cover" as it is, I look at it and say "da*n he was really flying down that stretch.".

Generally, leaving space for things to move into is a good idea. I think this is an exception.

Also, panning got plenty of motion blur on the wheels and background, why would anyone want motion blur on the bike/rider?

Nice use of thirds.