The upgrade has just been released and I know that it is iOS 5 as that is the version that has been tested in the developer program. It has been released today as it is required for the iPhone / iPad AirPlay feature.
It may not say iOS 5 in the version, but that is the underling code base.
Apple appear to be having download issues generally, my iPad iOS 5 download has just errored.
Seems they are overloaded as expected. Not surprising as we all have many gigs of software to download.
iPad, iPhone, Apple TV, OS X 10.7.2, iPhoto, etc, etc.
Just noticed my Apple TV is now at step 2 of 2, so further than before.