I think people throw around ideas like this without considering the side effects. One problem is that if you remove our bipartisanship you introduce the possibility of electing someone where a small group of extremists is able to gain a majority vote because the rest of the candidate pool is so spread out.

Imagine an election with 15 candidates. 14 of them are democrat/liberals and 1 of them is Neo-Nazi. Who wins? This might be an extreme case, but if you divide up the voting sensibilities of the majority, you risk the chance that a smaller group of like-minded people may overrun the race.

Similar instances of this have occurred in the past, such as in France's 2002 election, where Jean-Marie Le Pen made it to the second round of elections because he was running against many other candidates:

http://en.wikipedia.org/wiki/Jean-Marie_Le_Pen

http://en.wikipedia.org/wiki/French_presidential_election,_2...

I'm not saying that a partied system is a good one, but it's does solve some problems that should be considered before you dismiss the idea entirely.

edit: added link to french election page