Thanks for the reply.
I completely agree that keeping the 'Next|Finish' text in view at all times in a footer is doing right by the user.
I'm sure that its current height makes certain that people don't miss it at the bottom of their window, but perhaps something slightly less tall might still serve well while preserving proportional integrity visually?
I suppose that it doesn't fit with the modern Microsoft design language, but a translucent footer with opaque text also crossed my mind as a way to hint to the user that there was more to be scrolled down to, while keeping 'Next'|'Finish' in view at all times.
Most of the screens in upload are quite short, but the third with the photo license, title, description, etc. is longer and I feel that unless the user knows what to expect from previous incarnations of Photosynth or is the curious type, they may miss that there is more to the page to scroll down to.