Although other community members like binarymillenium figured it out first, their processes were a bit manual.
Our fellow Photosynth user, Christop_Hausner has written an incredibly easy to use program that will do all the work for you. You can download it here: http://pspcexporter.codeplex.com/ .
One other cool project I've seen was Kean Walmsley's Photosynth browser for AutoCAD 2011, but it isn't as ready to use as Christoph's exporter is for the average person.
If you'd like a decent default model viewing program to use, the general consensus seems to be to get Meshlab.