I've been searching for a very nasty bug that hits all versions of IE up to 8 in CSS.
Basically the bug is the following: there's a div (#inner) placed inside an other (#container). If I give opacity to the inner element in IE8, the font color of the inner div (#inner) will become the same as the background-color of the outer (#container) element.
The solution was the same for the infamous anti-aliasing bug related to transparency: add
position:relative to all elements, and thus: all bugs are fixed.
If you use
filter: progid:DXImageTransform.Microsoft.BasicImage(rotation=3); -ms-filter: "progid:DXImageTransform.Microsoft.BasicImage(rotation=3)";
you need to add a background image to make IE render the font correctly.