One challenge that my proposed federal amendment would face is it would encourage the formation of third parties -- people with a large but still fractional agenda such as greens, white supremacists, socialists, or religious nutjobs of various stripes -- aiming to grab a few electoral votes. For example, in California this time around, even with the huge turnout, a mere 181,000 votes would have gotten you a seat at the Electoral College. In 2000, Ralph Nader would have picked up two electoral votes in California, and one each in a handful more states.
What's wrong with that, you ask? The problem is that a proliferation of third parties, while good for extending the scope of political debate in the country, would also greatly increase the likelihood that no candidate would end up with an EC majority. And that would mean that the election would be thrown to Congress, where the President would be chosen by the arcane (and even less regionally fair) mechanism of giving each state delegation one vote -- one each for Texas, New York, and California; and one each for Wyoming, Delaware, and Alaska. Over time, as third parties arose in large states to go after the fractional interest groups, having Presidential elections decided this way would likely become the norm rather than the exception. And although the small states might love that outcome, it would hardly be good for the republic.
A couple of additional provisions to the amendment could short-circuit this result. One option would be to have a run-off between the two leading EC vote getters. This solution has the disadvantage of stretching out the voting beyond a single day, with all sorts of unpleasant logistical and procedural implications. A better option would be to create a default provision in the amendment whereby, if no one were to achieve a majority in the EC, then whoever has a plurality of the popular vote nationally would be declared President.
From a policy perspective, this is in essence a compromise between Josh's proposal and my own. It has the advantage, however, of having a prayer of actually getting passed.