The Supreme Court affirmed the approach taken by the trial court with respect to the burden shifting nature of the Special Committee.  The trial court was found to have been correct in assigning the burden of proof only after the trial had occurred.  As the Court reasoned:

The Court of Chancery could not decide whether to shift the burden based upon the pretrial record. After hearing all of the evidence presented at trial, the Court of Chancery found that, although the independence of the Special Committee was not challenged, "from inception, the Special Committee fell victim to a controlled mindset and allowed Grupo Mexico to dictate the terms and structure of the merger." The Court of Chancery concluded that "although the Special Committee members were competent businessmen and may have had the best of intentions, they allowed themselves to be hemmed in by the controlling stockholder's demands."

The inability to resolve the burden until after the trial resulted in "practical problems for litigants".  Nonetheless, it was an inevitable consequence of the standard.  

In affirming the lower court, the justices tried to minimize the impact of their decision.  The Court described the shift in the burden to the shareholders as a "modest procedural benefit" (emphasis in original).  In other words, boards gained only a modest value in seeing the burden shift.  Moreover, the assignment of the burden was not invariably outcome determinative as the facts in Americas Mining illustrated.  See Id.  ("The Court of Chancery concluded that this is not a case where the evidence of fairness or unfairness stood in equipoise. It found that the evidence of unfairness was so overwhelming that the question of who had the burden of proof at trial was irrelevant to the outcome."). 

In fact, a "modest" benefit probably overstated the value that came with the shift in the burden.  Defendants asserted that the failure to determine the burden shifting issue prior to trial would discourage boards from using special committees.  The Court disagreed, citing the value of special committees. 

That argument underestimates the importance of either or both actions to the process component—fair dealing—of the entire fairness standard. This Court has repeatedly held that any board process is materially enhanced when the decision is attributable to independent directors. Accordingly, judicial review for entire fairness of how the transaction was structured, negotiated, disclosed to the directors, and approved by the directors will be significantly influenced by the work product of a properly functioning special committee of independent directors.

In other words, the benefits of a "properly functioning special committee" weren't modest, they were insurmountable.  If the committee was properly functioning, the burden wouldn't merely shift.  IN effect, shareholders would be subject to an irrefutable presumption of fairness.   In effect, the standard of review was not really entire fairness but the business judgment rule. 

Some primary materials from the Chancery Court are posted on the DU Corporate Governance web site.