The Founding Fathers were quite concerned about the mercurial whims of the masses and constructed the Constitution in such a way to safeguard government and promote stability. They succeeded beyond their wildest dreams. (Note the French are on their fifth Republic) The Electoral College was a construct that served as a filter against direct election of the President. It has, over the past two centuries, evolved into a process that distributes power towards smaller and medium sized states as each state has a minimum of three electoral votes (2 Senators and 1 Representative). The first-past-the-post system of allocation is key to protecting this important power re-distribution. Proportional representation will limit the clout of smaller states as candidates will be incented to campaign more on a national scale and concentrate in larger states.
Colorado Democrats' attempt to enact a referendum that will allocate Colorado's electoral votes proportionally (see link in title), and make that allocation retroactive to this presidential election, therefore merely dilutes Colorado's influence over future elections. The Colorado Democrats want to try to shift some of the state's electoral votes to Kerry in what may be a close election, as the link above indicates. As Republicans realized after pushing enactment of the XXII Amendment (which term-limited presidents, a regrettable occurrence in 1988), be careful what you wish for.