Quoting Robert Douglass <rob@robshouse.net>:
I could export my blog posts from one site and import them into another site and keep the id.
You could "keep the id" but IMO you shouldn't. You don't know if there may be an existing id in the receiving DB. The ID is unique to each DB and existing values should not be merged from one DB into another. That said, the only correct method for merging data from one DB into another is to use the API for the receiving DB so that the foreign key constraints match appropriately (even for those DB engines not supporting foreign key constraints). In Drupal's case the nid should be removed so that a new nid is created or the uid should be removed so that a new uid is created. An import/export API should take into consideration this fact and allow for the removal of the ID columns on import or export. Earnie -- http://for-my-kids.com/ -- http://give-me-an-offer.com/