If you think Twitter hasn’t been able to keep pace with the momentum of the rest of the online world then guess again. They’ve just announced that they’ve acquired Posterous. It’s a blogging platform that has private and social aspects to it and you can share photos, videos, etc through it. Effectively, this can lead to Twitter getting a hold on a private social market that’s tied in to their open social Twitter market and this can be a pretty big growth stream for them.

I don’t use Posterous so anyone who does feel free to chime in but this seems like a big move for Twitter and shows you where they are headed over the next year.