Spaghetti
Nobody ever say so, but for so many years now I have been confronted with DWH spaghetti projects. No matter the tools used, somehow it seems an utopia to create a clear architecture / ETL / Datamodel in time.
The problems are huge. People come and go. Without a clear view of what new people have to do they start their own way with their own vision and methods. The beginning of the end. And where does it end? High and rising maintenance cost, disappointed users etc etc. » More: Spaghetti code