If I am right, using the Blobstore API (http://code.google.com/appengine/docs/quotas.html#Blobstore) requires apps to have billing enabled. However, do application need to have billing enabled to use db.BlobProperty() ? http://code.google.com/appengine/docs/python/datastore/typesandpropertyclasses.html#Blob
If I understand this correctly, then I only need billing enabled when using the Blobstore, but I can store binary data with BlobProperty() without having to use the Blobstore.