While this feature is nice in theory, I find the current implementation far more annoying than useful. The problem is that the transition is not smooth. When the header is in it's normal place everything goes smoothly and once it detaches and sticks to the table it runs smoothly, but trying to scroll the page stops & then jumps when it hits the actual moment of detaching.
I've seen a number of other sites do a similar setup where an element stays in it's normal place on the page until you scroll beyond that point and then it sticks to a given point on the user's viewing area. However, the other ones I've seen all did so smoothly. I have no idea what they do differently. (Unfortunately I don't have any specific sites to link to as examples, though I'll post them here if I encounter any again.)
edit: I found this: http://css-tricks.com/persistent-headers/
If you click the demo link & scroll it, you'll see that the header transition from static to fixed seemlessly & unnoticably.
edit 2: Here's an example of a seamless transition: http://www.part15.us/forum/part15-fo...egulations-law