Vault 3 was recently updated. New in version 0.50: Vault 3 now works much better with file synchronization programs such as SugarSync and DropBox.

Configure your synchronization preferences in the Options / Settings dialog:

If you check the "Check for documents" checkbox in the above dialog, when you have a given Vault 3 document open in Vault 3, and that file is updated outside of Vault 3, the following dialog box will be displayed:

Download Vault 3.