Friend and colleague Timo Hannay at Nature took notes on Creative Common’s guru Joi Ito’s presentation there. Money quote:

CC licensing increases demand but cannibalises sales. So there’s a trade-off depending on the demand and sales of any given piece of work at any given time. The questions about CC licensing are therefore practical ones about what, who and when – not a religious decision. (Though for scientific and certain other types of content, CC believes in free access.)

In these situations, the communities often police themselves, enforcing social norms such as attribution and non-commercial restrictions. [Joi gave a Star Wars fan fiction example.] In some cases, fans create derivative versions (e.g., subtitled films) to encourage the publisher to release an official (paid) version, removing the amateur version when they succeed.