Like it or not, the enduring image of the CNN/YouTube debate is Billiam the Snowman. The question itself represented a frontal assault on the prime directive of candidates in debates: control what you can about the environment. I believe that the candidates’ staff probably felt they had an understanding with CNN that there would be a certain level of respect in the questions. The Democratic campaigns probably also decided to do the debate knowing something like this would happen.
From CNN’s point of view they probably needed to have at least one irreverent question in order to feel like they’d been true to the Net nature of YouTube. Let’s review the question:
"As president, what will you do to ensure that my son will live a full and happy life?" gesturing to a mini snowman at his feet.
The Republican response has been clear: Mitt Romney said "I don’t know that it makes sense to have people running for president
answering questions posed by snowmen." With that statement, Romney said what the other Republican candidates have been thinking as they made noises about "scheduling conflicts". If the Republican candidates skip the CNN/YouTube debate, there probably won’t be any lasting damage. However the inability to engage with the general public in other, less controlled channels will be a flaw that will make a notable difference in the results of the general election for whomever becomes the nominee.
For more on Billiam, see the WSJ story, "Snowman Video Chills Some Politicos"