I've just gotten a reply from the Duke University registrar's office in response to my question:
During the CCMBA, our advisers told us that our degrees would be conferred on 30 December 2010. ACES, however, still lists us as "active in program." How will we get official notification that we’ve earned our MBAs?
The registrar's reply:
Thank you for your email. We do not add the degree to your record until the University Trustees meet to officially confer the degrees. They generally meet in mid-January and the degrees are posted to the record usually in late January with a confer date of December 30th. Please keep a check on your academic history in ACES and you will be able to see when your degree has been posted.
So, we're not yet officially masters of business administration, but it's probably all right to put the degree on our résumés.
 ACES is the registrar's computer system.