Old, and heavily overrated. It throws away a lot of pictures (where it isn't sure where to place them), needs *massive* overlaps and quite some computation. It will never work with holiday photography, but you need a pro taking the photos or use some archive such as flickr.
Granted, for such a set of photographs it is impressive, but the claims of turning this quickly into an end user product are marketing blah-blah.
The actual research was probably done at the University of Washington, http://phototour.cs.washington.edu/
Maybe old, maybe overrated, but still cool. You gotta hand it to whoever came up with that, the last time i stopped and said 'wow' to something i saw on a computer was xgl/compiz ;)
As for comparison to xgl/compiz, there was a slight difference, that xgl/compiz was real, as opposed to PhotoSynth that just works in the lab... But otherwise, yes, I was like "Wow" too.
oh I see, it installs as a plugin instead of an extension, nsiPhotosynth.xpt in firefox\components directory and dlls in C:\WINDOWS\SYSTEM32\Photosynth