A tip for all the new people who have joined: I highly recommend clicking "Subscribe to new topics" on the categories you're interested in. (Or the highest level one, since it applies to all subcategories as well).
It's very easy for new communities to lose traction because people forget to come back and check for new posts! Subscribing will make you get email notifications of new topics, which will remind you that there's stuff going on and people worth responding to. (Note that you can also subscribe to individual topics to see new posts in them)