For mobile devices we definitely need a login api to login into the photosynth server...so as to then at least upload. 
There also needs to be good documentation with the service.

wafe5068, I was under the impression that any mobile Photosynth app would come from the Photosynth/Bing Maps team themselves. Do you know something that I don't?

Having a way to contribute panoramas (or possibly synths) from third party apps would be very cool, but I haven't seen anything that suggests this yet.

We just released an iPhone app today! http://blogs.msdn.com/b/photosynth/archive/2011/04/12/announcing-the-mobile-photosynth-app.aspx