Paradroid is on the right track.
If you look at the feed of new submissions, you'll see a mix of synths and panoramas being uploaded. On that same page, you can filter to only view photosynths or only view panoramas.
Ever since photosynth.net was launched in August of 2008, people who were new to Photosynth almost universally always started out by shooting synths as though they were shooting a panorama. I find that it generally takes a fair bit of patient discussion with someone before they realize that Photosynth needs you to move around your subject instead of just standing in one place and turning.
Since Photosynth was never intended as a panorama viewer and because people continually tried to upload panoramas, Photosynth finally talked to their friends at Microsoft Research who had previously created the panorama stitcher Image Composite Editor (or ICE, for short) as well as the world class panorama viewer, HD View, to develop a panorama viewer for the Photosynth website.
This was also beneficial for people who used ICE to stitch panoramas because prior to the photosynth.net integration, ICE users had to have their own website and know how to upload their own files to a server that they had paid to store data on in order to share their panoramas online with HD View. When ICE introduced photosynth.net integration in 2010 March it meant that all you needed was a free Photosynth account to share your panorama with the world and in a few simple steps broadcast it into Bing Maps.
Even though photosynths aren't panoramas and panoramas aren't photosynths, ICE solved the problem of people trying to use Photosynth as a panorama viewer. Although ICE is a world class panorama stitcher, it is completely automated with no real way to manually help the program if it makes one or two small stitching errors in an otherwise beautiful panorama. For people who were accustomed to other panorama stitchers such as PTGui, it was irritating that the only way to upload panoramas to the Photosynth website was through ICE when they already had perfected their panorama in a tool that allowed them to manually hint until everything was just right.
Toward the end of 2010 November, Microsoft Research released a plugin for Photoshop which allowed you to publish a panorama to the Photosynth website. This meant that the door was opened for anyone to export their perfect panorama from another panorama stitcher to Photoshop and simply upload from Photoshop to the Photosynth site. Since the Photoshop plugin is so new, the submissions that people are uploading with it are being heavily featured on the Photosynth homepage, but actual photosynths are still being uploaded every day.
To upload panoramas from ICE or Photoshop, you do still need the Photosynth app for Windows (which is used to construct and upload photosynths) installed to do the uploading to your Photosynth account.
Panoramas are often very beautiful and are certainly easy to navigate, given that there is nothing to do but turn around and zoom in and out. When crossed with the Photosynth viewer's highlights feature, though, the way that the virtual camera swoops and zooms around the panorama is really smooth and enjoyable.
All of that said, Jenko makes a very true statement that photosynths are really the next step and offer something that no panorama yet can: movement through 3D space and the beginning of taking stitching into 3D via Photosynth's point cloud. Navigating a synth is certainly more complex than navigating a panorama for the time being - mainly because each and every synth you ever load will have been shot with a completely unique camera motion around the scene, but synths are definitely still my favorite. The point clouds that we see in Photosynth today are what the Computer Vision industry refers to as sparse reconstructions. Photosynth has essentially done the absolute minimum amount of 3D reconstruction possible - just enough so that they can recover the camera positions to arrange all the photos in 3D space. If you look for Photosynth competitors, there is definitely a lot of work going on with photogrammetric 3D reconstruction and even projects that reconstruct more than a Photosynth point cloud, but almost none that are focused on sharing 20 gigabytes per free account of your photos online with their full resolution available to be zoomed into, even though the Deep Zoom Image format is publicly published and several open source viewers exist.
My takeaway basic advice for beginning Photosynth photographers would be to circle the things that you want a 3D construction of with no less than 24 photos apiece and then be sure you get photos looking from one object to the next and walking between them. This is very different from shooting a panorama.
For a panorama, your camera's lens should stay in the exact same place in the air while it looks in all directions and doesn't zoom or change the distance at which it is focusing if you want a perfectly stitched panorama.
For those who are concerned that the future of Photosynth is in danger of being lost to panoramas, don't be afraid. I've collected links to videos of Photosynth team members talking about where they plan to take Photosynth going forward. You'll find the links in the left column of this spreadsheet which can be downloaded and resorted by the column of your choice: http://docs.com/XFO The most recent talk that I've found can be found viewed at: http://bit.ly/are2010blaise
To view the small percentage of synths and panos which have been geo-tagged, visit http://bit.ly/photosynthcoverage and remember: if your favorite park, restaurant, school, market, store, house of worship, statue, tree, garden, theater, museum, etc. isn't on the map you can photograph, process, and publish it to Bing Maps within a single afternoon. Help your community out and share your neighborhood with the world.
That's the story!