If you are hoping for a Metro-style Photosynth app, then I sympathize, however it is not absolutely necessary... yet.
If you are hoping to view synths and panoramas (and hopefully spin movies soon http://bit.ly/spinmovies ) in IE 10 Metro, you'll need to wait until the HTML5 Photosynth viewer is finished, since Metro IE doesn't allow plugins. ( http://photosynth.net/discussion.aspx?cat=a6bad539-de7d-4a16-8c4d-b143f7d5f984&dis=82ce7d6a-bb10-4511-b8dd-00568e3c95a6 )
In the announcement for Read/Write World earlier this year in April ( http://bit.ly/readwriteworld ), Photosynth's former architect, Blaise, announced that his team is working on creating a single viewer that opens photosynths, panoramas, spin movies, and many other image types, so work is underway, but it's difficult to say when we'll see this.
So far, the only public sign of this work is the HTML5 panorama viewer for mobile Safari: http://bit.ly/psfhtmlpv