I found a wired issue in Mobile Safari as demo http://mocheng.github.com/demo/translate3d.html
There is one page translate3d_iframe.html inside translate.html as iframe. Elements in translate3d_iframe.html has style -webkit-transform: translate3d(0, 0, 0) to force 3d acceleration.
The interesting result is that the 3D-ed element would always displayed on top of other elements event it has lower z-index.
What is more interesting: the 3D-ed element is just displayed to be on top of other elements. You can still tap on the menu item "hidden by" 3D-ed element (alert message is shown on tap).
This can only be reproduced in Mobile Safari.
Is there anyway to workaround it? I just felt that web developers have to know how iOS browser works to attack such type of issues.