The OS X Mountain Lion Up-to-Date upgrade will be available at no additional charge from the Mac App Store to all customers who purchase a qualifying new Mac system from Apple or an Apple Authorized Reseller on or after June 11, 2012.
Customers who purchase a qualifying Mac between June 11, 2012 and the date when Mountain Lion is available in the Mac App Store will have 30 days from the date Mountain Lion becomes available to make their Up-To-Date request.
Customers who purchase a qualifying Mac after Mountain Lion becomes available in the Mac App Store will have 30 days from the date they purchase their Mac to make their Up-To-Date request.
When Mountain Lion becomes available in July, come back to this page to request your copy of Mountain Lion.
OS X Mountain Lion is expected to drop around July 25th. Once that happens eligible users can go to this page to get your free update.
Read More [via CultofMac]