I'm not doubting photosynth is a 'cool' tech, however, I can't see its advantages to panorama which is quite popular at present.
Also, for e-commerce, it has two problems.
1. it usually does not work for many objects which has salient SIFT features
2. photosynth can provide "rotation" click mode, however, it's not better than a quicktime object movie using panorama.
I think the most feature it has is to provide point cloud, but for a buyer or a seller, point cloud even 3D model is not so useful to pay for photosynth(as a business model)
In fact, I'm dounting whether MS is going to earn from photosynth, and how many photosynths is on the web? How many users keep using this service? I'm looking up the alexa ranking of photosynth, and it's only 41,769 which means not so many users using it.