POLITICS: Third-Party Candidates - "worthwhile" or "waste of time"?

I've known a couple of people who were very pro-Third Party, y'know?

From their perspectives, America's two-party system is flawed (though, perhaps not as much as America's two parties, themselves). As far as they're concerned, if we, as voting Americans, really want to affect change, we need to seriously consider voting for "Green" or "Independent" candidates.

Of course, a lot of folks respond by saying that voting for anyone other than a Democrat or a Republican is basically throwing your vote away (except, maybe, in local elections). A lot of folks also think that these third-party candidates have spoiled races, like the 2000 Presidential election, by pulling more voters away from the Democrats and, thus, making it easier for Bush to get into office.

Each of these points can and has been debated by others until the cows came home... and left again. But what do YOU think?

Is it worthwhile to vote for a third-party candidate - maybe like we sometimes support independents in industries (like filmmaking), thus giving them more and more power to affect change directly and indirectly?

OR

Is it a waste of time to vote for a third-party candidate - maybe because they can't win, anyway, and we take the chance that we'll allow a really poor candidate to win (perhaps leading to unnecessary wars)?


Whatever your reasons, which do you believe third-party candidates are: "Worthwhile" or "Waste of Time"?
Why?