Allright, I'll hijack the thread a bit because I have the same question as the OP. I'm an experienced web developer, some experience with Joomla, novice with GJ.
I do understand the concepts and workings of GJ quite well. One of the things that I can't grasp is how categories work.
Is a category a container for a set of groups with similar interests? Are categories only virtual containers, or can I do something more with them, eg in the frontend? Put another way: why do I need categories?
Thanks, and thanks for a great framework/plugin set!
Mark.