I really couldn't agree more on this topic. In addition, beside the huge motivational effect of building something useful that you want to have for yourself, in my experience you´re also automatically making sure that the user experience is right and you really love the product. So it´s kind of a switch from "I need to build this for this user-guy to work with" to "I want to craft this in a way, so I can love it."

Sumup: Being your own user enables you to convert user experience from just useable to lovable.