Here is the mail from customer service, I've just replied to this mail to follow up with them:
The $10.00 Online Gift Certificate will be delivered via email to you on
December 26, 2009 to the email address associated with your $100.00
BN.com Gift Card / Online Gift Certificate purchase on Barnes
Visit
www.bn.com and click on the options that appear in the upper
right-hand corner to view information about your order.
We look forward to your next visit.
Sincerely,
Donna
Customer Service Representative
Barnes and Noble
http://www.bn.com/