I would say that, while IE8 is by far more standards complaint than its predecessors, It still lacks several css 2+ selectors and has incomplete implementations. e.g. lack of :before, :after, :focus, etc.
I can't seem to consider IE8 in the same level as Firefox and Chrome. I'm looking forward to IE9 though - the problem is that it's probably only going to be widely used a lot of years after the official release.