There's a project out there whose photos will likely never be shown in Photosynth which is the California Coastal Records Project run by Kenneth + Gabrielle Adelman. http://www.californiacoastline.org/
The reason I say their beautiful datasets will probably never appear in Photosynth is because they feature a "Proud to be Microsoft free" logo on their homepage.
They have multiple sets of photos from different years that pan down most or all of the California coastline that would make an amazing Wall synth (if you could view it as one continuous synth + not in little 200 photo chunks).
Will Photosynth ever be able to present a dataset of this size if someone who loves Photosynth shot our own as the Adelmans have?
I will admit that their datasets are a little on the sparse side for Photosynth, even if they were willing to contribute, but I wish things could be worked out with them.
I'd love to browse Bing Maps' large swaths of Bird's Eye View photos like this.