The team is very friendly, and they have an incredibly generous free quota as compared to other services (2 GB of files/database, 5 GB/month of bandwidth, and 16 MB of Redis - per app). They use plain old WSGI for the server, Postgres for the database, and they'll install any packages you put in a requirements.txt file, so no lockin. Haven't used Django with it, but so far my experiences with Flask are great.
http://devcenter.heroku.com/articles/python
There's even extra love for Django specifically:
http://devcenter.heroku.com/articles/django
Absolutely no lock in -- Heroku runs any WSGI app with a completely standard Python/virtualenv/pip runtime. It uses Python 2.7.2 currently.
And of course, the entire Heroku ecosystem is available, such as PostgreSQL and Redis databases, New Relic analytics, etc.