Every "format" on the internet has its strengths and weaknesses. Each is focused on a certain type of interaction.
Discussion & Debate
In my opinion the single-thread discussion format (that this forum uses) is still the best approach for a ongoing topic, and works well up to a certain size (maybe ~300 posts or so). Talking about recent events, or having a debate on a certain topic where there is back and forth, and you want to reference previous posts. Twitter messages are too short and useless. Facebook doesn't bring the right people together and the discussion aspect doesn't scale as well. I still like vBulletin (and other UBB-clones) the best.
Question & Answer:
Where the "PHPBB" interaction format start to break down is when people want to search existing content of questions and answers when they are looking for a answer to a straightforward question.
My favourite structure for this sort if information is how Stack Overflow
Comprehensive Knowledge Repository
When you want an well developed article, I think the Wiki format is the best interactive medium that will produce a great end-product (in the form of an article). Clearly Wikipedia has been tremendously successful there. Other good examples are WoWWiki where you have a specific (game related) knowledge repository.
Facebook and Google+
I quite like this format of having "circles" of people who automatically see your updates. I don't think this discussion format will tend to encourage in depth discussion, but this format would tend to do two things: include people who you know personally, and keep responses short. It also has the side effect of doing a great job with pictures and (apparently) multi-player games. I know a certain someone who is hooked on Facebook Bejewled and needs to play every week to beat her friends scores. Human beings love sharing and commenting on pictures, and they also love proving that they are better than their friends at a game.
I'm not a twitter fan. I think Facebook and (especially) Google+ are better than twitter in important ways. First, they don't have that silly character limit, and second, they are better that sending out a one-to-many "IM" style message where the many isn't
"the world!" I often have something to say to my peer group.
Where are things going next? I dunno, I think the communication mediums will be more specialized; not generalized. A long time ago on the Internet I had email and that was it
. It was how you did business, and if you wanted a discussion forum, well, you just created mailing lists using email. Listserv.
I'm not smart enough to be able to say anything intelligent about what's next specifically, but I think the trend will continue in that we'll have more options on how to communicate, not less.