http://volokh.com/posts/1179142697.shtml There will be posts on the topic all week, just thought you'd find it interesting.
The author raises interesting points, though I don't think that the disciplinary record of World Cup 2006 was that worse compared to previous years. Introducing a different type of caution - "orange" card or something like that is a possibility, but it remains to be seen whether it will be effective. Soccer does not always adjust well to revolutionary changes in the rules, it arguably remains a more conservative sport than basketball or hockey.