I love the way you wrapped the file with a button and changed it`s opacity to 0.
What I don`t understand is how you managed to prevent the user from clicking on the input field outside the button.
When I`m looking at the field with FireBug I can see it extends on the left of the widget but when I try to click it I can`t.
How do you do that?
There is one more invisible element (a mask) that covers this area.