The Creative Commons "noncommercial" restriction being vague is quite important. A lot of content is being published under the CC licenses, and it would be good

The Creative Commons "noncommercial" restriction being vague is quite important. A lot of content is being published under the CC licenses, and it would be good to get some clarification. For example, would an ad-supported re-publishing of the content be against the license? Anyone know of authoritative definitions of this clause?