[Joel]

It's not creating a new template per se, as much as it is that you can "fake" a .gtemplate file by changing the file extension of a .graffle file (which will keep its window size and position saved) simply by changing the file extension.

There isn't very much terribly different between the two file formats, however when exporting as a template or creating one from scratch, OmniGraffle will strip out the window position information as it's bad form to have your new documents always in the same spot, according to Apple's Human Interface Guidelines.