With the platform-as-a-service revolution getting into full swing, developers (especially in start-ups) have more options for creating and deploying applications without the hassle and more extreme cost of setting up and maintaining infrastructure.
Dion Hinchcliffe at ZDNet compares Amazon's approach to providing infrastructure services to Google's. He found that Amazon's set of services is more flexible but not as integrated as Google's App Engine.
What if you realized that you didn't want to host your application on Google App Engine anymore? Good luck; almost everything you are given access to is proprietary--that means all your data is locked into BigTable in a format that isn't like a traditional relational database. It's also very tempting to use the APIs Google provides to interface with things like Google accounts.
On top of that, you will be using the "Webapp framework" that Google built that makes writing Python applications really nice--but good luck porting that to another language or putting it on a machine of your own.
On the other hand, Google is just trickling out its platform-as-a-service with support for Python. Support for other languages will follow. Whether Google would support other databases in its cloud remains to be seen.