While this talks mostly about data warehousing, oftentimes denormalization is useful for everyday web app data storage. If your web app (usually on Postgres) is mostly frequent reads and rare writes (most web apps are) — there's no excuse for your pages to load slower than a static site. Store your data as normalized as you want, add a denormalized materialized view, update it on writes, render pages based on the view.

Of course I'm talking about 95% of the apps where this is acceptable, not 5% where table locking can cause problems, leading to the need for concurrent update handling.