5 years ago my internet history would reveal a list of online-communities to which I belonged. Each community website was a CMS (PHPNuke, phpBB with a lot of plugins, or e107 if I was the admin) and had all the content related to that theme. The latest news, the downloads (or torrent) section, a forum for us to discuss stuff, a gallery, some articles and miscellaneous things that vary from scene to scene.
Today I get all my downloads from ThePirateBay (at least until now), all my news from Google Reader, I write all my long stuff in my blog (wether it is portuguese politics, music or even geeky posts), I write all my short stuff to twitter, and all my photos to flickr. Although there are tagging capabilities, you cannot group people and friends, so you share everything that matters to a specific group. The sense of online communities is dying with these services.
The only service in which communities play an important role is the one that survived from the Ice Age of the Internet: Email. I subscribe to a few mailing-lists and almost all of them are themed. I really want communities back, and services that empower them. The Internet is either getting Semantic and abstracting a lot of stuff, or it is going back from services to hosted applications.
I do miss the way I met new people with the same interests. Much more personal than adding the people facebook suggested you.