SAN FRANCISCO ( TheStreet) - Microblogging site Twitter is now valued at $8 billion, CEO Dick Costolo said Monday night at the Web 2.0 conference in San Francisco. That valuation is based on the company recently raising $800 million in a two-stage funding round, Costolo said, adding that Twitter is not looking towards a near-term IPO. "We don't want to be beholden to an IPO window," he said. "I want the company to go public when the company is ready and prepared to be a public company, and not at the whim of some window." Twitter sees around 250 million Tweets a day, Costolo said, compared to 100 million in early 2010. It has 100 million active users, about half of which log in daily. The company is also squarely focused on building its mobile presence, which it is growing 40% each quarter. Sign-ups for Twitter have also tripled since the release of Apple's ( APPL) iOS 5, which has deep integration with the service. Twitter has no plans to link back up with Google ( GOOG) to show real-time Tweets in Google's search engine, Costolo said, adding the two parties couldn't agree on terms. -- Written by Olivia Oran in San Francisco. >To follow the writer on Twitter, go to http://twitter.com/Ozoran. >To submit a news tip, send an email to: firstname.lastname@example.org.