Initial vision:
Unplugged
The Drupal synchronization module
The Drupal Synch module
- knows that when it last synched you are at node 253, user 43, comment 422, etc...
Logs, configuration settings, installed modules etc. could - should - be one way, from the server to your offline Drupal.
offline to server and back
Drupal 6 dumps the sequences table: implications?
Drupal 6 has the database handle sequences. This may make it harder for Unplugged to do its thing.
Not really though.