Posterous was just acquired by Twitter:
Posterous Spaces will remain up and running without disruption. We’ll give users ample notice if we make any changes to the service. For users who would like to back up their content or move to another service, we’ll share clear instructions for doing so in the coming weeks.
This means Posterous is going bye-bye. I wonder how long Twitter will keep Posterous online. As has been suggested, this seems to be more of a talent acquisition than a sign of things to come. I highly doubt that Twitter feels threatened by Tumblr.