When I first saw the original demo I was really impressed, but now that is been released I feel like it hasn't advanced enough since that demo to really be useful. I tried a few random synths when the server was having problems, it looks like it isn't being hammered any longer so I ought to try it again soon when I'm using a compatible OS.
Overall it's confused and muddled to use and look at- like a broken quicktime VR.
Photosynth seems to work best in terms of interface and experience when it is simply a panoramic viewer of stitched together images- where all the images are taken from a point of buildings or scenery around the viewer. It's easy to click left or right to rotate left or right and have the view intuitively change. But we've had photostitching software that produces smooth panoramas that look better than this for years, so there's nothing to offer here.
When viewing more complicated synths, the UI really breaks down. I don't understand why when I click and drag the mouse the view rotates to where I'd like, but then it snaps back to where it used to be when I let go of the button. It's very hard to move naturally through 3D space- I think the main problem is that the program is too photo-centric: it always wants to feature a single photograph prominently rather than a more synthetic view. Why can't I pull back to view all the photos, or at least a jumble of outlines of all the photos?
It seems like there is an interesting 3D point cloud of points found to be common to multiple photos underlying the synth but it can't be viewed on it's own (much less downloaded...), there are always photos obscuring it. The photograph prominence is constantly causing nearby photos to become blurry or transparent in visually disruptive ways.
Finally, it seems like the natural end-point of technology like this is to generate 3D textured models of a location, with viewing of the source photos as a feature but not the most prominent mode. Can this be done with photosynth-like technology or is all the aspects I don't like a way of covering up that it can't actually do that? Maybe it can produce 3D models but they all come out horribly distorted (so then provide a UI to manually undistort them).
Hopefully they will improve on this, or another well-backed site will deliver fully on the promise shown here.