Forcing ID's in GAE is a bit harder, and i don't think that web2py has support for that yet.
also note that once the database gets to be of significant size the import/export features will have to be written to run as taskqueue tasks on GAE so that they can run for 10 minutes instead of 30 seconds for web based requests. if you are only using GAE consider looking at the GAE bulk import/export tools. they fix ID's, and can run on infinitely large datasets. http://code.google.com/appengine/docs/python/tools/uploadingdata.html
