Here’s the wording from from Twitter’s blog post:
Today we are welcoming a very talented group from Posterous to Twitter. This team has built an innovative product that makes sharing across the web and mobile devices simple — a goal we share. Posterous engineers, product managers and others will join our teams working on several key initiatives that will make Twitter even better.
Posterous is perhaps most closely compared to Tumblr — sort of a cross between a blogging platform and a sharing service. Some reports suggest Twitter is mostly interested in the people at Posterous, but the decision to keep Posterous Spaces alive seems to pour some water on that theory.
Twitter says Spaces will stay alive “without disruption” and the company has promised to “give users ample notice if we make any changes to the service.” There’s a FAQ page with a few more details, including Twitter’s plans to let Posterous users know how to make backups of their content and/or export that content to other services like Tumblr, WordPress or Blogger.
There’s more discussion on Techmeme.