Well this makes me happy, I got my 40gb iPod a few days ago, and to my delight the sisters old 10gb 3rd gen works perfectly fine in my new dock
It does not fit snugly because of the size difference, but other then that it works fine, so if you have an old 3rd gen with no dock, you can buy a new iPod with the new iPod dock and it should work fine with your old iPod.
I have not yet tried the reverse though.
I have not yet tried the reverse though.