I've been quite impressed by the content of the Creating Passionate Users blog which uses research in psychology and metacognition to explain why some products or ideas can (like Moodle) build succesful markets and communities while others fail.
As well as helping to understand Moodle's current success, it's got a lot of interesting content for those pondering how Moodle (the product) and Moodle.org (the community) can continue to grow.
Some examples:
