We use Google App Engine because we lack serious sys-admin skills, and GAE abstracts all that away from us. Also, the datastore was much easier for us to understand and hack than relational databases.

For project hosting, we use hosted-projects.com because it gives us SVN+track+bugzilla and wires them together, and they have good tech support. I also like Beanstalk, but it doesn't come with a bug tracker.