-- Sorry I probably wasn't clear in my enthusiasm.
You don't _need_ a Cray to be able to synth these. In my case I had thousands of pictures, and some software that the PS team gave me to try synthing offline. It was faster for me to iterate through my pictures down to a set that 'worked' by using the cray to synth them.
Once I had the 'good' set of images, I then used the 'standard' way of doing it -- uploading to Photosynth.net and having it build the rover synth.