You can save and restore your Photosynths but it requires some preparation. I recently upgraded my iPhone to 5.0.1 and was required to set it up as "new" which means that I would lose all my Photosynths. But I was able to restore them all of them using the following procedure:
1) you must have access to the file structure of the phone.
I have a jailbroken iPhone and use netatalk (available from Cydia) which shares the phone on the desktop (Openssh also works to ftp into the phone)
2) Find the location of the Photosynth app in /private/var/mobile/Applications
(SBSettings helps find the app)
3) once you have found to the location, copy all 6 items to your computer's hard drive (Photosynth.app, Documents, Library, tmp (folders) iTunesMetadat.plist and iTunesArtwork (files) . Or better, synchronize them occasionally.
4) Keep these files updated!
When you need to restore, replace all items (app is not necessary) into the same place on the iPhone.