Whether you are developing a new dimensional data warehouse or replacing an existing environment, the ETL (extract, transform, load) implementation effort is inevitably on the critical path. Difficult data sources, unclear requirements, data quality problems, changing scope, and other unforeseen problems often conspire to put the squeeze on the ETL development team. It simply may not be possible to fully deliver on the project team’s original commitments; compromises will need to be made. In the end, these compromises, if not carefully considered, may create long-term headaches.
via IntelligentEnterprise : Kimball University: Three ETL Compromises to Avoid (printable version).