Quick tip to disable IE8 standards mode...
skin/common_files/customer/meta.tpl
Replace...
Code:
<meta http-equiv="X-UA-Compatible" content="IE=8" />
With...
Code:
<meta http-equiv="X-UA-Compatible" content="IE=edge,chrome=1">
...which should enable rounded corners and other CSS3 effects in IE9 etc.
Not sure why QT are still doing this, even in v4.5.0 !