A cynic might argue that the key difference in this case was that, for a change, the ISP's, and not merely defendants, were challenging the subpoenas; but of course we all know that justice is 'blind'.
An ingrate might bemoan the Court's failure to address the key underlying fallacy in the "John Doe" cases, that because someone pays the bill for an internet account that automatically makes them a copyright infringer; but who's complaining over that slight omission?
A malcontent like myself might be a little unhappy that it took the courts ten (10) years to finally come to grips with the personal jurisdiction issue, which would have been obvious to 9 out of 10 second year law students from the get go, and I personally have been pointing it out and writing about it since 2005; but at least they finally did get there.
And a philosopher might wonder how much suffering might have been spared had the courts followed the law back in 2004 when the John Doe madness started; but of course I'm a lawyer, not a philosopher. :)
Bottom line, though: this is a good thing, a very good thing. Ten (10) years late in coming, but good nonetheless. - R.B. )