The solution is based on an add-in. Data changes are audited internally on a hidden spreadsheet and then synchronized to a database when the spreadsheet closes (if the connection is available).
The solution has the ability to prompt the user to integrate any new spreadsheet created (i.e. on-the-fly integration), but requires locking away the embedded VB code (automated naturally).
It is an efficient audit, that also promotes the use of external add-ins (which is better for reusability). It has virtually no impact on performance and requires at a minimum a database where the audit information will be to stored.
Tested on Office 2003 & 2007 successfully