ubuntu-sso scripts use #!/usr/bin/env python

rtg@delorean:/usr/lib/ubuntu-sso-client$ head -n 1 *
==> ubuntu-sso-login <==
#!/usr/bin/env python

==> ubuntu-sso-login-gtk <==
#!/usr/bin/env python

==> ubuntu-sso-login-qt <==
#!/usr/bin/env python

==> ubuntu-sso-proxy-creds-qt <==
#!/usr/bin/env python

==> ubuntu-sso-ssl-certificate-qt <==
#!/usr/bin/env python

http://www.debian.org/doc/packaging-manuals/python-policy/ch-python.html
The preferred specification for the Python interpreter is /usr/bin/python or /usr/bin/pythonX.Y. This ensures that a Debian installation of python is used and all dependencies on additional python modules are met.

If a maintainer would like to provide the user with the possibility to override the Debian Python interpreter, he may want to use /usr/bin/env python or /usr/bin/env pythonX.Y. However this is not advisable as it bypasses Debian's dependency checking and makes the package vulnerable to incomplete local installations of python.

At least once this resulted in ValueError: Unable to guess signature from an empty dict for a user with a custom python installation in /usr/local.