Good news for all who wanted to get a Mac NOW but don't want to miss out on the up-and-coming OS X Mountain Lion. Apple have issued a notice serving that all Apple purchases made between June 11, 2012 and the date when Mountain lion is available in Mac App Store, will have 30 days to make their request and get Free Update.
That being said, I urge if you haven't registered your Apple products and purchases to it registered to be entitled for the free upgrade.
Of course, all purchases you made between the date aforementioned are entitled for the free upgrade as long as you registered your product accordingly.
For more details, please go to this link OS X Mountain Lion Up-to-Date Program