I have to admit this is becoming increasingly attractive to me. My objection to most third party runs is that they are usually from the crank wing of either party Nader/Perot, and they are not going to win simply throw the election to the other team for a symbolic loss.
The current situation leaves moderates on either side forced to ally themselves with the right or left wings in order to gain an electable majority. I can't recall a viable run from the center that did much, but this one might. My biggest objection to John McCain is his un-constitutional campaign finance reform with my Senator. What a perfect example of unintended consequences stemming from good intentions and bad policy.
National Security, Smaller Government and Judges are my issues. Both McCain and Lieberman are very solid on National Security, and I don't know that either would be too bad on the other two as well. The fun would be how this would mess with the Congress. They could play both ends against the middle and just the total disruption of the status quo would be healthy for our democracy.
So let's watch as the Dems and Repubs sling mud left and right and then POW! right out of the middle come the mavericks. Sounds interesting for sure. (h/t K-Lo)