Twitter co-founder Ev Williams took the stage today at the Web 2.0 Summit in San Francisco, wrapping up the three day event.

John Battelle, interviewing Williams, admitted that at last year's Web 2.0, he was "needling [Williams] endlessly about what your revenue model was." But "now you have an answer" - promoted tweets and promoted accounts. It's a "promoted suite of products," said Williams.

"A Promoted Suite of Products"

While some reports peg these promotions at about $80,000-$100,000 of revenue per day, Williams said that "I don't do the math." He did say that there is "way too much demand for the supply." He added that Twitter has purposefully kept these new promoted tools small. And the response, says Williams, has been "interesting"

"We've taken an organic part of Twitter and given companies an opportunity to optimize what they're already doing on Twitter," he said. And the company has found that the promotions have increased conversations by about three to six times, beyond just the time-frame when the promoted trend actually runs.

"We can't just put stuff in front of people if they don't care about it," Williams said, stressing the importance of making something useful for users and suggesting that this is why it took the company a while to roll these promotions out. Twitter monitors the impact carefully, assessing the "resonance score" for every Tweet in order to measure how these ads perform.

The Value of a Tweet

"Have you learned enough to say you have a strong revenue model?" asked Battelle. "The math looks good," said Williams, noting that advertisers are coming back. "It's done better than we'd expected."

The other revenue model is access to the Twitter firehose, a reference in part to the announcement today to Twitter's partnership with Gnip. Williams stressed that some of these deals are not simply about revenue. Instead, it's a matter of distributing Tweets - for search engines and for users.

Is There Money in the Twitter Ecosystem

Will the firehose be consumed by Facebook? "You should ask Mark that," quipped Williams, "and you've missed your opportunity." Williams did say that he was frustrated that Facebook had blocked some of Twitter's connections to Facebook. "They see their social graph as their core asset," says Williams, who says that Twitter and Facebook are looking for ways to work together. But, "we'll see."

Dismissing rumors of a possible investment from the Russian investment firm DST, Williams said that Twitter has plenty of cash in the bank.

Cash might not be so flush for those in the Twitter ecosystem, as Williams indicated that the company planned to continue to build out the product. When asked which areas would be safe for third-party developers, he said "I don't know." Twitter has been as seen encroaching on those developers' territories with, for example, its acquisition of Tweetie in order to make an official iPhone app.

As ReadWriteWeb reported in September, Twitter plans to have its own analytics platform available as well. It's no surprise then, as Williams admitted today, that Twitter can already gauge users' influence based on their Tweets and retweets.