We've previously covered the release date for Mango, and this is pretty much confirming with what we've already published (September 15th). On the Windows Phone Developer Podcast (episode 33), Ryan and Travis Lowdermilk explain that they've heard from a number of sources that the upcoming major update will be arriving next week.
While this is still up in the air, it's starting to piece together like a jigsaw. I'm sure most of us are more interested in how efficiently the roll out will prove to be. Listen to the podcast (if you haven't already) below and keep an eye out for the 34:20 marker where the Mango goodness is discussed.
Source: Windows Phone Dev Podcast, thanks Sander for the tip!