Twitter's long-rumored funding round is finally real: Spark Capital and Amazon (AMZN) founder Jeff Bezos (via Bezos Expeditions) led the round, with existing investors Union Square Ventures and Digital Garage also participating. Spark's Bijan Sabet, an active Tweeter, joins Twitter's board.

Co-founder Biz Stone didn't get into financial details on his blog post, but the numbers are probably similar to the ones floating around in May -- a $15 million round at a "bit less than" a $100 million valuation.

What will Twitter do with the money? Obviously the company's first priority is building out its infrastructure -- so Twitter can keep growing without the downtime and interruptions all too familiar to avid users.

"Twitter will become a sustainable business supported by a revenue model," Stone writes. "However, our biggest opportunities will be worth pursuing only when we achieve our vision of Twitter as a global communication utility. To reach our goal, Twitter must be reliable and robust."

By the way: The company says it's reworking the broken Flash service that powered our Community Twitter page; In the meantime, you can still follow our Tweets here: The human-powered SAI Twitter account; our automatic, articles-only feed; managing editor Peter Kafka; and myself, Dan Frommer.

See Also:
Twitter: Developers Love Us!
Ten News & Information Twitter Feeds You Should Follow
Corporate Twitters Worth Following - And Some You Should Avoid