I've only ridden two CO's (2009 and 2010) and I never once rode a paceline in either one. There is really no need - you've got all day to get to the next camp and plenty of support on the way. It's tough to enjoy the scenery and engage with your riding companions when you are in a paceline and have to focus on that wheel in front.
Nice pics everyone - thanks for taking the time to post. Looks like CO2011 was a great time!