Blocks-based programming holds potential for end-user developers. Like all visual programming languages, blocks-based programming languages embody both a language design and a user interface design for the editing environment. For blocks-based languages, these designs are focused on learnability and low error rates, which makes them effective for education. For end-user developers who program as part of their professions, other characteristics of usability, like efficiency of use, will also be important. This paper presents a usability analysis, supported by a user study, of the editor design of current blocks-based programming systems, based on the Cognitive Dimensions of Notations framework, and we present design manoeuvres aimed at improving programming time and effort, program comprehension and programmer comfort.