[mariana]

you can host webapps written in Python and use Django on there (or just almost any other Python framework). That doesn't look like vendor lock-in to me, if they decide to shutdown the service, you can move your webapp to another place, like your very own server.

[paulgb]

FWIW, even if you use django, the database is still Google's proprietary db.

[mariana]

That's right, and because of that my applications deployed on there have 2 branches: one using Google DB and other using data models provided by Django. IMHO, developing this way is pretty easy and prepare you to migrate your apps if necessary.