Let me break it down in pieces and explain the parts

#!/bin/sh
if [ $(git diff HEAD@{1} HEAD --name-only | grep -E
'base-requirements|prod-requirements' -c) -ne 0 ]
then
    $VIRTUAL_ENV/bin/pip install -Ur prod-requirements.txt
fi

Essentially what the above is doing, is doing a git diff, grep'ing to see if my base-requirements or prod-requirements files changed, and if they did, doing a pip install prod-requirements (which includes base-requirements) to ensure that all my dependancies are met/installed.

## if a settings file or a models file change, restart uWSGI
if [ $(git diff HEAD@{1} HEAD --name-only | grep -E
'conf/*.py|web_site/*/models.py' -c) -ne 0 ]
then
        source venv/bin/activate && fab restart_uwsgi
fi

Like the comment says, I'm checking to see if a settings file (located in web_root/conf/) or if a models.py file changes, I want to restart uWSGI (necessary for these changes to take affect.

The next piece:

 ## if a migration file exists, syncdb and migrate
 if [ $(git diff HEAD@{1} HEAD --name-only | grep -E
 'web_site/*/migrations/*.py' -c) -ne 0 ]
 then
     source venv/bin/activate && fab syncdb && fab migrate_all
fi

You don't need to run a syncdb or a migrate (if you're using South) every time you deploy. So I check to see if a new migration file exists, if so, then I run a syncdb and a migrate.

And last, sadly a "dirty" hack (sort of). By default, nginx uses www-data user/group to serve files and I'm actually managing my server as root (cause real Sys Admins use root! :P)

## if a file changed in web_site/ change owner to www-data:www-data
if [ $(git diff HEAD@{1} HEAD --name-only | grep -E 'web_site/' -c) -ne 0 ]
then
   source venv/bin/activate && fab change_owner
fi

What the above does, is checks to see if a file changed in the web_root directory, if it did, it changes the owner and group (this ensures that nginx can serve the necessary files).

Git hooks have proven to be a time saver. Taking quite a bit of redundancy out of the process/steps necessary to deploy/manage my django projects.

These of course are written to work with my workflow/habits and may not fit everyone, but my hope is to help those who haven't established a workflow, or to give a starting point for everyone else, and can tweak here/there as necessary to support their workflow/habits.