I seem to have jumped the gun in reporting that problem, as I figured the solution out myself a few moments later. Apparently QBDIR can't be a parent folder of where you're building the GUI from. That is, I had QBDIR=/tmp while the GUI was being built from "/tmp/api/python/qb/gui". When I changed QBDIR to /Applications/pfx/qube, it built properly.
Sadly, now I'm having runtime errors:
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] <_FuncPtr object at 0x1005cbbb0>
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] Traceback (most recent call last):
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] File "/tmp/api/python/qb/gui/dist/qube.app/Contents/Resources/__boot__.py", line 153, in <module>
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] _argv_emulation()
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] File "/tmp/api/python/qb/gui/dist/qube.app/Contents/Resources/__boot__.py", line 151, in _argv_emulation
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] _get_argvemulator().mainloop()
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] File "/tmp/api/python/qb/gui/dist/qube.app/Contents/Resources/__boot__.py", line 75, in mainloop
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] stoptime = Evt.TickCount() + timeout
7/25/11 3:51:10 PM [0x0-0x40040].org.pythonmac.unspecified.qube[555] AttributeError: 'module' object has no attribute 'TickCount'
7/25/11 3:51:10 PM qube[555] qube Error