This paper studies organizational learning effects in open-source programming projects. Working with data from the Apache and Mozilla projects, the study focuses on three aspects of open-source development. The first is the use of the open-source approach as a hedge against system complexity. The second is the adaptive learning mechanisms realized by the debugging process. The last is the learning curve effects of project-specific experience on bug cycle times. The results indicate that while open-source development is subject to positive learning effects, these effects are not universal, with some projects deriving more benefit than others.