One problem I've had in designing the web site from a usability aspect is how to let people easily cast preferential votes.
The other thing one has to consider with this issue is dealing with a large number of alternatives. When working with a small number, and interface like Rob Brown's works extremely well.
But, consider what happens when the number of alternatives grows to a large number...basically beyond what can be displayed on the screen all at once.
The ability to sort the potential selections becomes important and it may be useful for the initial list of alternatives that each voters sees to be random.
A user will not want to press the 'move up' button a lot to get it into the proper location. I would guess that somewhere beyond 10 alternatives is the threshold - someone else mentioned drag-and-drop to help with this.
I'm sure there are other issues that could be listed here that I have not yet considered.
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