Should not a database be denormalized for reading performance?
Okay, here goes a total "Your Mileage May Vary", "It Depends", "Use The Proper Tool For Every Job", "One Size Does Not Fit All" answer, with a bit of "Don't Fix It If It Ain't Broken" thrown in:
Denormalization is one way to improve query performance in certain situations. In other situations it may actually reduce performance (because of the increased disk use). It certainly makes updates more difficult.
It should only be considered when you hit a performance problem (because you are giving the benefits of normalization and introduce complexity).
The drawbacks of denormalization are less of an issue with data that is never updated, or only updated in batch jobs, i.e. not OLTP data.
If denormalization solves a performance problem that you need solved, and that less invasive techniques (like indexes or caches or buying a bigger server) do not solve, then yes, you should do it.
