App Engine data migration?

My biggest reservation concerning App Engine is data migration. What if I want to move my app and its data off-of App Engine. And let's say I have a half-gig of data spread out over tens of millions of records. I can't simply write a python app to dump it in a single request because it would terminate before completing. So would I have to resort to writing an app that dumps it in small batches? Has anyone see this issue discussed anywhere?