Linking synths?

You're both right on. Having watched every video that I could find that relates to Photosynth a few too many times, I can say that they are definitely planning both of the features that you two mention. My personal unofficial theory is that if you geotag your synths, when Live Labs introduces synth merging, it will automatically look for synths that are geotagged as nearby and then analyse the image features from one synth against the image features of any neighboring synths to try to discover any common objects which will allow the system to position the point clouds far more accurately in Virtual Earth. I look at Birds' Eye View in Virtual Earth 3D and am 100% positive that we are meant to swing from those aerial photographs straight into our synths in the future.

Here are some links to quotes that should make you very happy to read.

In later updates we hope to give you the ability to stitch synths together, and then walk them seamlessly. - David Gedye

For the next little while, we'll mostly be prioritizing community features over fancier visuals. Path planning and my-photos-in-context are high on the list, though. - Blaise Aguera y Arcas

As a result, sharing (and the eventual combining of synths) is very easy and natural. In my mind, that's one of the most important design decisions that we made. - Gary Flake

At some point, I think we'll have to offer some basic editing capability so that users can remove photos from a synth or even adjust the aggressiveness of the matching algorithms so that they have the option of removing false positives. - Gary Flake

We are pushing the data into a central location so that we can eventually stitch synths together. If the product was designed so that everyone was encouraged to make little "island" synths, then there would be little hope that all of the different synths could be combined into a larger, unified, collection. Our sincere hope is to make a system that continuously improves because of user contributions, thereby increasing the value for everyone and in a highly non-linear way (think about how your vacation photos and my vacation photos are, well, just okay, but together they are vastly better. Now multiply this by millions of people.) - Gary Flake

They are really good ideas (editing of synths, merge different synths, etc). - Dan Hou

yes -- we are VERY interested in allowing individuals, groups, and the community to create bigger and bigger experiences. The basic way we are going to acheive this is by linking synths together and allowing you to walk -- as seamlessly as possible -- from one synth to the next. - David Gedye

Also, here are a couple of links to your fellow photosynthers who think like you do:

Location recognition/integration with other synths

What features should we add to Photosynth? (Just search this page for "combine", "merge", or "multiple")

Lastly, here are some of those videos that I mentioned. I'll list the timecodes for watching the bits about joining synths, but the whole videos are very interesting.

PhotoSynth: What. How. Why.
Blaise brings up multi user synths at 24:40 and then at 35:14 talks about a farther future where photosynth can connect web pages by connecting the photos in the pages.

The technology behind Photosynth
Blaise starts talking about what you're interested around the 15:30 mark here.

Drew Steedly and Joshua Podolak on Photosynth
Drew and Josh talk about coming up with ways of joining synths around the 29:00 mark here.

Photosynth and Seadragon offer a glimpse at the next great UI
Watch for 11:11 - 14:00 and 15:00 on

ShutterSpeed EP04 - The Photosynth Team
At 29:14 Nic Fillingham asks the same question that we have. Drew talks about joining through multiple synths of the same thing and Blaise talks about connecting neighboring synths.

There are also some early promotional videos from an older version of the Live Labs site that talk about the much larger future potential of Photosynth allowing you to jump into a photo on one web page and then jump back out through a related picture to the page that it came from. I'm not sure if this has been abandoned for the moment because of the copyright on people's photos and privacy concerns or not. Certainly this post from Blaise seems to indicate that they've shied away from that strategy to one of just combining photos that people have chosen to share already... at least for the time being.