when embedding a Flash object with the <object> and <embed> tag, there is an attribute called wmode. It seems that most of the time, wmode="transparent" is the same as wmode="opaque" as the Flash doesn't actually have any transparent color so that the bottom HTML element is to be shown. As a result, opaque should be faster than transparent since it requires less processing for transparency, yet most of the time i see Flash object embedded with transparent instead of opaque.
opaque is needed so that other HTML element won't be covered up by the Flash object (such as a menu item that pops up an extra sub-menu won't be covered up by the Flash object).
By the way, is there formal documentation for wmode's opaque, transparent, and window? I was only able to find blogs that describe it but not the formal documentation. thanks.