I heard something about this on CNN the other day. What they were saying is that this is great except that there is an expectation that anyone forced to do this will fight it in court as being illegal because the EPA is an executive agency and gets it authority from the Whitehouse instead of Congress. The basic belief is that the EPA doesn't have the authority to enforce standards like this without Congressional authority.
I suspect Congress will be taking this issue up anyways so it may be a moot point. It'll be interesting to see how this plays out and one way or another will undoubtedly be good for all of us.