The Green party down here in Australia have turned into a viable political force. They've picked up several seats in our Senate, giving them the balance of power. All through the power of, "Everyone else sucks, I'll vote Green".
Once upon a time, we had a wonderful little party known as the Democrats. Campaigning on the platform of "We'll keep the bastards honest", they were able to retain the balance of power and prevent the extremes of Government from pushing through retarded legislation. Then the leader sold out on a big issue at the time, the introduction of the GST. Last year, the Democrats announced that they were disbanding permanently, after failing at every subsequent election.
The moral of this story is, if you're going to be a third party, be a third party. Tread that fine line with care, because either side of you is a fifty mile drop into a pit of acidic spikes and flaming, explosive piranhas.