"When there becomes a need for someone to build software that allows user to customize their own interfaces, it means we haven't been doing a good enough job at developing our user interfaces so users wouldn't feel the need to do this." I don't agree with this. Many applications have many different types of users, and designing a single interface for all of them means cutting things that only work for some of the users. User customizable interfaces free the developer to provide all the functionality and let the user decide what works best for them. Firefox is a superb example of this, particularly with the popularity of Firefox extensions. I think many users know better how they want to use an app than the developers do.