Scott Jones wrapped up a research paper titled "Investigation into modular design within computer games".
Scott Jones recently completed a lengthy review for Staffordshire University on modular design practices in the industry. It covers almost everything you need to know about modular design. Everything from history to technical limitations and advantages, to practical and theoretical uses.
Don't let the word count fool you, its chocked full of images, great examples and solid explanations. For anyone who has wanted to know more or is just wondering what is modular design you should check it out, its a great collection of insight.