I ashamedly admit that I've fallen behind in keeping up with the latest features of IE8. I found out IE8 supports mutable DOM prototypes (although in typical IE fashion, the support is limited) thanks to Nicholas' quick write up. Still, it's more than we had, but an incomplete implementation is still incomplete. Other features caught my eye:
I remember reading about most everything else, other than the mutable DOM prototypes of course. I think it's time to get a VM setup and install Beta 2.