[By Sudarshana Banerjee]

Twitter has acquired Posterous, a blogging service started in 2008 by Stanford graduate Sachin Agarwal, who is now CEO of the company. Posterous investors include Y Combinator, Redpoint Ventures and Trinity Ventures, along with other angel investors and entrepreneurs. Mr. Agarwal is joining Twitter as product manager. He says he will be focusing on product, instead of worrying about also running the company.

“Posterous Spaces will remain up and running without disruption,” assures Mr. Agarwal in a blog post. “Posterous engineers, product managers and others will join our teams working on several key initiatives that will make Twitter even better,” says Twitter.  “Acquisitions have given us people and technology that have enabled us to more quickly build a better Twitter,” the company adds.

It looks like Posterous will continue to be around, but chances are the former Posterous team will now be focused on Twitter more, and the site might slowly and lingeringly become a also-ran in the coming days.

Why Twitter? Mr. Agarwal explains his decision in his Posterous space post.

There is no better fit for Posterous than Twitter. The opportunities in front of Twitter are exciting, and we couldn’t be happier about bringing our team’s expertise to a product that reaches hundreds of millions of users around the globe.

Plus, the people at Twitter are genuinely nice folks who share our vision for making sharing simpler. Everyone is passionate, excited, and truly believes in the product and the leadership.

Apple and Twitter have a lot in common: a great sense of product and design, amazing leadership, phenomenal growth, and a great culture. Of all the places I could imagine working, Twitter ranks the highest. (Think about how much I would hate working at Google!)

It’s fitting to be going to the only company Apple chooses to integrate deeply with. Apple has definitely picked a side in social networking, and it’s Twitter.

I’m happy to be at a company based in San Francisco. And in fact, the new Twitter offices are just *2 blocks* from my house. It couldn’t get any better than that.

And I’ll get to work with my good friends from BackType, who were acquired by Twitter last year.

Posterous reportedly has around 15 million monthly investors. The size of the acquisition was not shared.

[Image Courtesy: Posterous]