Nice series. I think the key is knowing what to log and why. I have been involved with logging where everything was logged because we could and I don't know that anyone ever looked at the logged data. I have also been involved with situations where changes were logged and used on a regular basis to show the "history" of a product.

This is 1 area where I think DB2 at least on the AS400(iSeries) has SQL Server beat because you can query the journals (think transaction log) directly. It does store a limited amount of data, but in one place I worked we had a process that queried the journals and loaded a history of the product in SQL Server with virtually no impact on the DB2 database.