peanut and I are pretty big backers of the two-party system. Take New Zealand for instance, their conservative party will likely get 35% plurality, but they need 50% majority, so likely they will have to make deals with the green party (think of Lieberman caucasing with the democrats to the extreme), so, the conservative party, to stay in power, will make huge concessions to one of the most liberal groups in New Zealand. I think the third party system sounds pretty appealing, but in practicality in the American system, there's a reason they haven't gained weight.
edit: by peanut I meant dukenukem.