Twitter lands more big backers

How tweet it is. Twitter, the microblogging service that is changing how people communicate, has closed its long-rumored funding round.

Spark Capital and Amazon.com Inc. founder Jeff Bezos led the round, the San Francisco company’s third, with existing investors Union Square Ventures and Digital Garage participating. Spark Capital’s Bijan Sabet, an active Tweeter, joins the board.

Twitter, whose motto is “What are you doing?,” is not divulging financial details, but word is that it landed $15 million for a valuation of slightly less than $100 million.

Twitter will use some of the windfall to become more reliable. Never before have users been so upbeat about a service that goes down so often.

Wrote TechCrunch’s Mike Arrington: “They are the only service I know of where users rejoice when they simply manage to keep their service live.”