Bummer! - Lost my avatar in the great deletion, so I've had to try and create my own.
Third parties can be a problem unless they are politically strong - and few are (except for ones like the Greens in Germany). That's the current problem here in the UK as well, as you've got the two main parties, plus several smaller ones who mainly take votes away from the Labour Party, making it difficult for them to get into power. And that's usually the problem elsewhere - third parties tend to be left-of-center, splitting the vote there and making it much easier for those on the right to dominate, as there tends to be fewer right-wing parties, so the vote there isn't as split.
While the US really could do with a strong third party, I can't see how one could get into that position with how things are today. As a result, we're stuck with just the two we have now for the foreseeable future, and so any celebrity endorsements of third options really are misguided and (usually) damaging to the Democrats.