>In the last federal election in the U.S. you had the Libertarian Party, the Green Party and the Reform Party in addition to the two traditional parties.
>I've gotta believe that many seats were won with a plurality in that election.

Probably not. There are very few Congressional districts where any third parties would get enough votes to make a difference in the outcome, or to result in a plurality rather than a majority. It's my impression that most races aren't at all close. Many, many districts are so heavily populated with one major party or the other that sometimes you don't even get an opponent of the minority party.

Tamar