I've got all the vB4 rounded corners and drop shadows working in IE9.
Of course, I had to add them myself, since vB4 only has the moz and webkit variants. And incidentally the next version of Chrome doesn't use the webkit variants, it uses the "proper" ones, so vB4's rounded corners and shadows won't work in that either.
I'll be using images instead of the border radius property so i'm sure mine will display in ie9 there displaying okay in ie8. I would have rather used the border-radius but ie has always been in pain whenever styling.