I just download the data from one of my App Engine application by following Uploading and Downloading, I used this new and experimental bulkloader.py to download data into a sqlite3 database. You don't need to create the Loader/Exporter classes with this new method

It does explain how to download and upload, but, as for, uploading is only for production server. You have to look into the command line options, it's not complicated.

Here is a complete example to dump data:
$ python googleappengine/python/bulkloader.py --dump --kind=Kind --url=http://app-id.appspot.com/remote_api --filename=app-id-Kind.db /path/to/app.yaml/
[INFO    ] Logging to bulkloader-log-20091111.001712
[INFO    ] Throttling transfers:
[INFO    ] Bandwidth: 250000 bytes/second
[INFO    ] HTTP connections: 8/second
[INFO    ] Entities inserted/fetched/modified: 20/second
[INFO    ] Opening database: bulkloader-progress-20091111.001712.sql3
[INFO    ] Opening database: bulkloader-results-20091111.001712.sql3
[INFO    ] Connecting to brps.appspot.com/remote_api
Please enter login credentials for app-id.appspot.com
Email: [email protected]
Password for [email protected]: 
.[INFO    ] Kind: No descending index on __key__, performing serial download
.......................................................................................................................................................................................
.................................
[INFO    ] Have 2160 entities, 0 previously transferred
[INFO    ] 2160 entities (0 bytes) transferred in 134.6 seconds

And the following is for upload to Development Server using the sqlite3 database which we just download (not the CSV):
$ python googleappengine/python/bulkloader.py --restore --kind=Kind --url=http://localhost:8080/remote_api --filename=app-id-Kind.db --app_id=app-id
[INFO    ] Logging to bulkloader-log-20091111.004013
[INFO    ] Throttling transfers:
[INFO    ] Bandwidth: 250000 bytes/second
[INFO    ] HTTP connections: 8/second
[INFO    ] Entities inserted/fetched/modified: 20/second
[INFO    ] Opening database: bulkloader-progress-20091111.004013.sql3
Please enter login credentials for localhost
Email: [email protected] <- This does not matter, type anything
Password for [email protected]: <- Does not matter
[INFO    ] Connecting to localhost:8080/remote_api
[INFO    ] Starting import; maximum 10 entities per post
........................................................................................................................................................................................................................
[INFO    ] 2160 entites total, 0 previously transferred
[INFO    ] 2160 entities (0 bytes) transferred in 31.3 seconds
[INFO    ] All entities successfully transferred

You will need to specify the app id, which must match the Development server is running on.

This may be no need once the bulkloader.py is stable.