I contacted Barnes and Noble about the Nook for Mac not working with Mountain Lion OS and here is their response.
Dear Valued Customer,
Thank you for your inquiry regarding NOOK for Mac application.
Based on the situation you described, we feel that the difficulties you
are experiencing would be resolved best by contacting us by phone.
We ask that you call us at 1-800-THE-BOOK (1-800-843-2665) and select
option 2 for NOOK Support. We are available Monday through Friday from
8AM to 11PM EST, Saturdays and Sundays 9AM to 11PM EST. Customers
outside of the United States may contact us at 201-559-3882.
If you prefer to chat with one of our Digital representatives, please
click on this link:
http://www.barnesandnoble.com/nookchat
Please accept our sincere apologies for any inconvenience this may have
caused and we look forward to hearing from you.
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,
Brandon
Customer Service Representative - Digital Support
Barnes & Noble
http://www.bn.com/
Visit our NOOK Support site for the latest updates and downloads at:
http://www.barnesandnoble.com/nook/support/