Okay, here are a bunch of leads for you:
Old standby case studies include the invention of the GUI, Palm, Tivo, iPod/iTunes.
50,000 Americans die from medical error annually, including many from “death by decimal” in hospitals when nurses accidentally mis-program infusion pumps (one slip, and you’ve given a 10-fold overdose!) My company (Cardinal Health) makes “smart pumps” which put “guardrails” around that kind of slip. http://www.cardinalhealth.com/alaris/
The famous Florida Ballot design, which led people to unintentionally vote for the wrong candidate in the 2000 US presidential election.
There has been a lot of press about how difficult home entertainment systems are…
I also recall a study that showed how a huge percentage of wireless-routers were returned to the store after consumers couldn’t figure out how to set them up.
Motorola constantly gets slammed for their UI, and they’ve gotten press lately about their new easier to use UI (which I participated in.)
Hotel alarm clocks have gotten some press–and there’s been efforts to redesign them.
Kodak has been quite successful with their EasyShare digital cameras–they’re the only ones selling ease-of-use as a value.
The recent Sony PS3 vs. Wii is a great case study on how “fun” wins over “tech.”
The whole dot-bom phenomenon is littered with companies who succumbed to digital-darwinism, and poor-interface design was frequently their downfall (and why Amazon, Ebay, Google and others endured against numerous competitive threats.)
In the US, Intuit’s TurboTax software has totally disrupted the tax-prep business. They claim that more people now do thier own taxes using their “easy to use software” than go to all of the H&R Block (the biggest tax-prep franchise) combined.
The BMW iDrive has been repeatedly slammed in the press, and by Don Norman.
Microsoft recently killed “clippy” the social-interface agent from MS Office. They claim that their redesign is so easy to use, it’s eliminated the need. People hated Clippy almost as much as they hated Microsoft BOB.
Paper maps became disrupted by MapQuest, then later Google Maps and GPS for ease-of-use reasons.
The Apple Mag-Safe connector recognizes that tripping over power cords can be a bad thing.
Voice-recognition systems are replacing the old “press 1 for customer service” automated-telephone systems.