IE8 for developers was released today at Mix;
It would be great if someone could volunteer to test SilverStripe with it, noting that some bugs might actually need to be filed with Microsoft rather than with SilverStripe.
Add tickets to open.silverstripe.com with screenshots showing the problem and clearing explaining whether the CSS should be changed on our side, or given IE8 is claiming to have full CSS 2.1 support, whether IE8 is at fault. Then we can draw attention to your well-structured examples and improve the browser (perhaps!).
IE8 whitepages. Lots of bedtime reading.
ROC's summary of them: