Well our experience with browser releases shows that usually the Beta versions of the browsers are quite different in some manners than the official version - for example IE7, Firefox 2 / 3, Opera 9, Safari 3 / 4. After all, they are in Beta for a reason.
That is why we established practice to wait for the official browser release and then to provide an official service pack of our controls. There were numerous occasions when we "fixed" things to work in the Beta only to have to "fix" them again once the official version is released. For IE8 the same pattern was followed.
the Telerik team