While working for a related development project, I've written a book about online communities. It is called "The Social Web: An introduction to web 2.0 and its online communities". The book is on Lulu.com and sells for 14 Euros (printed) and 7 Euros (PDF).
I've also started a companion blog for the book, at http://www.socialwebbook.com. I'll post portions of the book in the blog, along with updated information. My plan is to keep the two blogs fairly separate (although I'll occasionally cross-post), so if you are interested in online communities from a non-developer point of view, you can subscribe that other blog as well. This is a short quote from the Introduction:
With this book my goal is to provide a birds-eye view of the social web, rather than focusing an a specific technology. Along with some theory, you'll find a lot of practical information, links to useful sites, and all you'll need to increase your online experience and create your own online presence, if you don't have one already.
Most of you probably know way more than I've written in the 70 pages of the book, but I think it provides an interesting summary also for many IT professionals. Finally, if you have suggestions about how to promote the book (which is well outside of the Delphi community, in which I know how to move...) let me know.