We already knew Twitter was a big deal, but now they’re throwing in our faces. The microblog has raised a whopping $200 million, giving Twitter a valuation of $3.7 billion. Yep. All those little tweets eventually amount up to quite a lot of money.

The funding comes from Kleiner Perkins Caufield Byers, and some other existing investors too.  As AllThingsD noted, Kleiner Perkins is the only new participant in the round, but it’s a significant member of the team now, especially as it pertains to Twitter’s new valuation.

As part of the deal, Twitter’s adding a couple of new board members, as noted in Twitter’s blog post that just went live:

“In the past 12 months, Twitter users sent an astonishing 25 billion Tweets and we added more than 100 million new registered accounts. In that time, our team has grown from 130 people to more than 350 today. We’re thankful for every Tweet, every account, and every talented employee who has decided to join the Twitter team. This week, we’ve got some big news to share.

As part of a significant new round of funding with investor Kleiner Perkins Caufield Byers and existing investors, we’ve added two new members to Twitter’s board of directors. Please join us in welcoming Mike McCue and David Rosenblatt.The experience these new directors bring to Twitter, along with this renewed investment, will help us continue to grow as a company and business.

2010 was one of the most meaningful years since Twitter, Inc. was founded in 2007. We operate on a principle that people are basically good—when you give them a simple way to express this trait, they prove it to you every day. We’re proud of what Twitter users have accomplished, we’re proud of our work, and we’re very proud of our team. Thanks for being a part of this work; it means a lot to us.”