Does anyone know how to upload a synth to facebook?

you can't, facebook applications don't allow frames

But you can still post it as a link to the synth, which is what I've done with mine.

DeepZoomPix has a facebook app that lets you browse and zoom your facebook albums using the cool tech. www.facebook.com/apps/application.php?id=2366023637

Photosynth wouldn't exactly use facebook photo albums to create synths, so the idea isn't directly transferable. But an ability to display synths in facebook would be great. It would be my number 1 request.

Further to my comment, the video preview of a synth on the front page of this site could be created by a user, in the same way that Virtual Earth (Live Maps / Bing Maps) lets you create a video of your POIs.

If the ability to create a video was made, this could be uploaded to facebook, or even better the facebook photosynth app could automatically display this video as a preview with link to the site

This is an interesting idea.  I wonder how large those video previews are allowed to be?

I know this is late, but recently found this mention in a Microsoft Blog. A photosynth for facebook called MySynths. Very cool app:

http://www.facebook.com/editapps.php#/apps/application.php?id=114216030046&ref=appd