Powersoft and Sybase have always recommended against storing your primary PBLs on a network driver for performance reasons. (Source Control is a different story, of course.) As you might guess, to render any object, PB has to read through all the ancestors of the class (e.g. window) and all the subclasses (e.g. controls) to be able to determine what all the attributes are and where all the scripts are.
If you're truly curious, you can get Microsoft's/SysInternal's Process Monitor, filter to the pb100.exe process name, and watch all the file accesses that go on when you open an object.
Good luck,
Terry.