OSX Lion comes with python 2.7 as default. Although App Engine will run on 2.7, it is safer to develop on the version of python that your live app engine instances are running on, which in my case is python 2.5 currently.
From a fresh install of Lion, I did the following:-
Installed xcode via app store
Installed Google App Engine SDK for Python, by installing google app engine launcher
(This contains the SDK and a launcher app).
Installed mac ports
In a terminal:-
sudo port -v selfupdate
sudo port install python25
sudo port install py25-pil
This means I can start my django server on python 2.5 using:-
python2.5 manage.py runserver
However if you want to run dev_appserver.py it will still try to use python 2.7 (which, unless you've installed it into your default python, will be without PIL)
you can use macports to set the default version of python:-
sudo port select python python25
Finally, you might want to set Python Path to /opt/local/bin/python2.5 in your Google App Engine Launcher preferences
after upgrading google app engine SDK to version 1.6, I was getting an import error "No module named _ctypes". I have now upgraded to python2.6 and this fixed the issue.