1. Politics - if, say, Republicans controlled the government of a solid Blue state, they could help their Presidential candidate by adopting P.R. vs. "winner-take-all." (And vice versa, of course, though Democrats seem much less comfortable with such bare-knuckles politics than Republicans.)

2. Attention - this, I think, is the prime motivator in Colorado. As a Red state, it doesn't get much attention from either Presidential campaign, as zero electors are up for grabs. If it went with P.R., though, one elector might be up for grabs, and if the election is close (as this one is shaping up to be), it could easily be worth campaigning in a few such states.

Ironically, I doubt Colorado's particular proposal will help Kerry. Since it's a ballot initiative, it'll probably only pass if Kerry pulls off the upset, in which case it will, of course, help Bush.

Dems will be happy if we get 4 Colorado EVs we wouldn't have otherwise had in 2004, bit it will haunt us when we surrender 45% of the West Coast EVs in 2008.  

The Republican criticisms are correct: it takes away power from the state that decides to go that way, that power stemming from pooling votes to a winner-take-all.

Since the GOP is likely to win Colorado, I don't particularly mind if they do it there.

But they are likely to open up this same can of worms in California, and I'd be very much opposed.

On the whole, I'd rather not.

As you mention, straight P.R. doesn't work well in states with a small, even number of electors (4, 6, or 8). Every election comes out even unless there's a landslide (although AZ was close to 4-3-1 in your example). So if this passes and Colorado loses a seat in 2010, they may want to repeal it.

The Amar Plan is a better solution.  It would simply award a state's electors to the winner of the popular vote.  If enough states did this, it would ensure that the popular vote winner was also the winner of the electoral college.  Further, it would effectively give voice to voters in other states; they might not be able to swing their state, but their vote, in addition to those elsewhere, would be able to swing the Amar states - and the nation - to victory.

However, much the same could be said for Texas, Florida, Ohio, Georgia, North Carolina, and almost every state from the Mississippi to the Rockies on the GOP side.

That presumes that those states would adopt this plan.  Texas, Florida, and Ohio certainly wouldn't; they lean Republican, and their Republican legislators wouldn't give up those more-likely-than-not Bush votes.  Georgia, North Carolina, and Mississippi might be better targets, being controlled by Democratic legislators, but it's simply too much of a risk.

More likely than not, this plan will be adopted by well-intentioned blue states, not red ones, and by splitting their votes, they'll ensure that Republican presidents are elected for the forseeable future, no matter what the popular vote is.

I really don't like the emphasis on 'swing states' as currently practiced.  I want the candidates to battle whereever they have to for a majority.  

This would largely do away with the Red State/Blue State thing, which isn't good for national unity.

I hope it passes in CO and other states for the next election.

On the other hand, introducing some form of proportional allocation of votes for a winner-take-all office would be worse.

If you want to go down the proportional allocation road, the most reasonable course is to go straight to election by plurality of popular vote.

And then you pray that no election is ever close enough to require a recount.