Jamie, just one hopefully insightful note: The synther is actually uploading your photos from the moment that the first photo is converted into a deep zoom image and zipped up.
If you type %temp%\photosynther into your Run command or Windows Explorer address bar when a synth is being made, you'll be able to see the parts of a synth as they're made. You'll see:
1) a log file for each synth processed,
2) an 'images' folder, filling with one .dziz file per input photo, and
3) at the very end of the scene reconstruction the deep zoom collection file [collection.dzcz] and the binary synth.bin file outside of the images folder.
Now, if you make a COPY (I don't recommend MOVING files while Photosynth is making them =) of any of the DZIZ files or the DZCZ and change their file extension to .zip, you'll be able to look inside with 7zip, WinRar, WinZip, or even Windows itself to see just what a Seadragon deep zoom image or deep zoom collection is really made of.