Customers who have purchased a Mac between June 11, 2012, and July 25, 2012, which is not equipped with OS X Mountain Lion can grab a free upgrade of latest OS X Mountain Lion.
Qualifying purchases between June 11, 2012, and July 25, 2012
Customers who purchase a qualifying new Mac computer from the Apple Online Store, an Apple Retail Store, or an Apple Authorized Reseller — or an Apple Certified Refurbished computer from the Apple Online Store — between June 11, 2012, and July 25, 2012, that does not include OS X Mountain Lion can upgrade to OS X Mountain Lion for free.
Click this link to participate in the program. Your order must be entered by August 24, 2012. Subject to terms and conditions.
Qualifying purchases on or after July 26, 2012
Customers who have purchased a Mac on or after July 26th, 2012 and their system is not equipped with OS X Mountain Lion are also eligible for the free OS X Mountain Lion update.
Click this link to participate in the program. Your completed order must be entered within 30 days of the date of your purchase of a qualifying computer (described in this offer).
You can also check out details about Qualifying purchases for OS X Server at Source.
See also:
Download Mac OS X Mountain Lion