According to T-Gaap, a source in the Bay Area has alerted them that Mountain Lion will be released on July 19 in the Mac App Store. The source has not leaked any information beyond this, however, this information makes sense as Apple released OS X Lion on July 20, 2011.
If you’re unaware, Mountain Lion was announced by surprise in February of this year and was discussed in-depth at this year’s WWDC event. Mountain Lion will bring a ton of features over from iOS to OS X such as Notification Center, iMessage support and more. When released, Mountain Lion will go on sale for $19 via the Mac App Store. This pricing is available to all Mac users who are running OS X Snow Leopard or Lion. Users who have purchased a new Mac on or after June 11, 2012, will be able to upgrade to Mountain Lion free of charge.