Converted from a series of comments in the Keep the Electoral College diary

(You know, this whole EC topic was last on my list of things to debate, but I'll take a stab at the third party issue. If this ends up being diary worthy, let me know or Brendan can use his awesome editor powers to transform it.)

It's tough for a third party to make much headway at all in our modern political system. Just glancing over the election results for citizens/voters who are still living, using 1936 as an arbitrary start point (and using Brendan's very cool link above) it seems that there were only three elections where a third party candidate had any showing in the popular vote:

Wallace in 1968 with 9.9 million / 13.53%
Anderson in 1980 with 5.7 million / 6.61%
Perot in 1992 with 19.7 million / 18.91%
[edited: I skimmed too quickly and left out Perot's 8% in 1996]

Nader, in the infamous 2000 election, only garnered 2.8 million / 2.73% of the vote.

Given that performance in the popular vote category, I would posit that the existence / nonexistence of the EC has no real bearing upon the success of a third party in our system. I very much doubt that the average voter thinks much about the EC when considering whom to vote for. I would also say that the candidates themselves do not base their decisions to run upon the existence of the EC process. And on those occasions where reasonably popular third party candidates arose (Wallace, Perot) I would say their popularity with the voting public had nothing to do with the existence of our EC process.

So, while one might argue that in some philosophical sense that the EC limits third parties, I think history shows that third parties are limited by much more practical and pragmatic factors, such as the entrenched two-party system.

Brendan suggested that the entrenchment of the two-party system is strongly aided by the EC. Perhaps it was initially. But regardless of its source, the two-party system is here now, and I doubt that the abolition of the EC would on its own change that.

Tlaloc added that the nature of the EC makes the failure of 3rd parties a self fulfilling prophecy. Perhaps that is true, but again, I cannot see where, today, removing the EC would make third party runs more viable.