Designing user interfaces is hard but designing products or services is even harder.  Why?  Because, with user interface design, you are only concerned about making user interfaces easy to use.  With product or service design, you have to also consider when, where, and how to make things difficult to use.

Services should be made easy to start using (i.e. one-click registration and subscription) but difficult to stop using.  Idiot designers will think in terms of walls, slopes, and mazes.  Smart designers will think in terms of incentives, habits, and addictions.

Fortunately (?!?), market moves too quickly for anyone except a handful of companies to do either properly, creating an atmosphere of tolerance for the mediocre or even torturous user interfaces, products, and services.