According to this post it may be between 7 and 10 inches.

I think that is too big to hold while I lay in bed and read and certianly not pocketable. But apparently it should take on the kindle.

The author of this article points out that Apple doesnt apparently have a problem with coming from behind and squashing the american market. She stated "Apple launched its first iPod three years after the first portable MP3 player arrived. Additionally, the iPhone hit the market five years after the first BlackBerry..."