Well, there's three groups at play here.
A group who have their 35L and generally very pleased with it and have been for a long time. My copy has paid for itself many times over the last 7 years of use.
Then there's a group of users who have just bought the new Siggi version. A great lens, but they like to make a big fuss over this new lens because they feel that they have a bargain...a better lens for less money. While it's true it's a fine lens, it's not up to the Canon L build standards and they are comparing a new design to one that's substantially older. The Sigma will always be a sigma and they have a reputation for mechanical failure and sloppy AF (a generalization and not pointed at this lens in particular).
Then there's a third group of guys who want a 35L but secretly want a new Canon version so that it's slightly better than the Siggi....which is totally silly when comparing the final images...
Either way, it's fun to see the drive and motivations in this thread. I'm in cat 1....but could easily tip into cat 3 once it's finally released and I get a big dose of lens envy