Post-save callback?

The hook has not been removed but splitted up into separate hooks for each $op.

See: http://api.drupal.org/api/search/7/hook_node

For post-save, you want hook_node_insert() and hook_node_update()

Currently Drupal core does not offer any hook to do actions after a node/entity is inserted/updated/deleted in Database. For example, you can not send an email mentioning the node after the node is inserted because Drupal uses SQL transactions and the node is not yet fully written to database when hook node presave is called so if for any reason the transaction is rolled back, users will receive a false mail.

So Hook Post Action module introduces several new Drupal hooks to overcome this limitation:

• hook_entity_postsave
• hook_entity_postinsert
• hook_entity_postupdate
• hook_entity_postdelete
• hook_node_postsave
• hook_node_postinsert
• hook_node_postupdate
• hook_node_postdelete

https://drupal.org/project/hook_post_action

I suppose hook_entity_presave could be the hook you're looking for, if you want to act before your node is updated :

Act on an entity before it is about to be created or updated.

Or, if you prefer acting after it's updated, take a look at hook_entity_update :

Act on entities when updated.