I don't think I've ever thought to do this. As I consider it, I don't think that I ever would for several reasons:
1. My style is one of expansion and technological superiority. By the time I'm ready to rid the world of all but a single rival, I'm pretty sure where things stand.
2. The updates that are given (most powerful, wealthy, happy, advanced, etc.) are a nice guide. I am not sure, exactly, what the powergraph takes into account, but when I try to take on the rival civs I'm looking to take out the one with the most techs, not necessarily the one with the most units or cities.
3. Embassies, Morco Polo's, and the UN. These can all give you pretty detailed info.
4. Just an ego thing - I wouldn't want to have a score permanently in my records where I was "Kevin the Doofus" or something.
Of course, my caveat here is that I am considering AI games only. I've never played a MP game (new to the board and really never knew that they were done). One would think that your human opponents wouldn't care for that.
Also, you'd probably consider your most powerful rival in MP the one with military units near your cities.
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Diplomacy - the art of
saying "Good Doggie"
until you can find a rock
[This message has been edited by Kev (edited February 28, 2001).]