it seems like
1) wmode="opaque" and wmode="transparent" are the same except transparent allows any transparent flash content to show any HTML content underneath it.
2) Otherwise, opaque and transparent are the same -- they both allow HTML element to be on top of the flash object.
3) The default wmode="window" and this value will make the flash object to be on top of any other HTML element.
4) transparent is slower than opaque, because it needs to process the transparent feature. as a result, most flash objects only need to use wmode="opaque" instead of transparent.
Can any Flash guru confirm that the above is true? thanks.
You pretty much hit the nail on the head there, yes.