Jinja2 is a great project and I wish it was easy to integrate with django.
I tried it through coffin http://github.com/dcramer/coffin and got hit by a few views from the contrib.auth models that had to be rewritten.
If you want to plug django-apps, you will have to patch and maintain them to work with Jinja2.
Coffin uses a nice trick to reload the view functions code with a Jinja2 version of render_to_response and RequestContext:
http://github.com/dcramer/coffin/blob/master/coffin/contrib/...
Note that django 1.2 will include 'Smart' if tags and Template caching if that is what you are looking for in Jinja2:
http://docs.djangoproject.com/en/dev/releases/1.2-alpha-1/#s...
http://docs.djangoproject.com/en/dev/releases/1.2/#template-...
If you're after Jinja2, wouldn't you find it more interesting to work with a minimalistic stack like Werkzeug, SqlAlchemy, couchdbkit... ?