After installing python-3.4.0.amd64.msi on Windows 8.1 x64, the "pip" command (and the versioned ones as well) only work for administrators. Regular users get this:

Traceback (most recent call last):
  File "C:\Program Files\Python34\lib\runpy.py", line 171, in _run_module_as_main
    "__main__", mod_spec)
  File "C:\Program Files\Python34\lib\runpy.py", line 86, in _run_code
    exec(code, run_globals)
  File "C:\Program Files\Python34\Scripts\pip.exe\__main__.py", line 5, in <module>
ImportError: cannot import name 'main'

The immediate reason is that the files in the site-packages/pip directory are created with no access permissions for non-administrators:

C:\Program Files\Python34\Lib\site-packages\pip>icacls __main__.py
__main__.py NT-AUTHORITY\SYSTEM:(F)
            BUILTIN\Administrators:(F)
            abc\Admin:(F)

Why that is, I have no idea. It can be fixed by running:

icacls path\to\site-packages\pip /inheritance:e /t
icacls path\to\site-packages\pip /reset /t

The /reset may be unnecessary.