Well I picked mine up this morning, to tell the truth I was a touch underwhelmed, it is short and fat and very heavy. I ran a few 'bench' tests on it vs the 17TS-E and the 16-35 f4 IS at f4, f5.6, f8 and f11. The IQ of the 16-35 f4IS is the best of the bunch at 16mm, but it doesn't tilt or shift and it doesn't go to '11'! IQ stays pretty solid at modest apertures even down to 11mm, the only thing that does become apparent is a little CA which is easily removed with one click in Lightroom.
As somebody who uses a 17mm almost every day and shift stitches regularly the initial impression is that 11mm is kinda ok, the 17mm stitch shift gives a much wider horizontal fov but loses the 3:2 aspect ratio. The projection distortion from the 11mm is not as bad as from the stitched 17mm. I haven't done a comparison between the 11-24 and a defished 15mm yet, I suspect there will be very little difference in fov, I will do the comparison soon.
So after a modest introduction to my new lens and a reality check as to its capabilities compared to my current solutions, I have to say I really like the images out of it and I feel for my own photography it will make me more adventurous. As so many have already said, the 16-35 f4 IS is a much better general ultra wide and I am seriously considering keeping mine for practical purposes, IQ and the IS, but the 11-24 isn't going back, it can take images no other lens in the world can!
Here are a couple of 11mm shots both at f4, not much point in posting much above that as the 16-35 f4 L IS would be 'better', first is the obligatory 'cat' photo and the second something more dynamic that shows the really nice colour and contrast even at f4.