Yes, it’s true. The Mango RTM build (7720) has leaked to the web via the XDA Forums and users have successfully flashed their devices to the new build, however, I would not recommend your average user flash their device as well as it can brick the device or even void out the warranty.
For those brave souls who know what they are doing, you can find instructions on how to take your device, no matter what build is currently running, to the RTM. For everyone else, I would highly suggest you do not try this at home and just be a little more patient for the official Mango release.
For instructions on how to flash your device to build 7720, click here.
Thanks for the tip Jon