Mango was recently released to manufacturing and since that point, everyone has been wondering when the platform would get released for public consumption. While there is a rumored date of September 1 as being the actual date, if you cant wait any longer, a supposed official build has leaked to the XDA forums.
And done. Zune back to retail copy and my HTC HD7 updated to 7720.
Not only that, Zune just found the official HTC update and is installing that to my phone right now.
So, after seeing that, I would say this is pretty official.
While some users are reporting success of updating others are running into trouble too. Of the users who have updated to the new build, there are no new noticeable new features as of yet. Although it has only been a short time, so it could be possible that new items may be uncovered in the near future.
Installing a leaked build on a Windows Phone device is a risky move to make. This unsupported update (as of right now) could cause issues when you get the official update at a later time. Heavy caution should be taken and if you do go down this path, you should understand that this could permanently brick your device.