Microblogging service Twitter has reportedly closed a $15 million Series B funding round, according to Om Malik of GigaOM.
Malik estimates that it will bring the company's valuation to about $80 million and that the round is led by a new investor rather than existing investor Union Square Ventures (though the latter is participating). CNET News.com originally reported late in April that Twitter had signed a term sheet for either $15 or $20 million.
But even as Twitter's valuation reportedly escalates, and it slowly breaks into the mainstream from Silicon Valley (Oscar-winning screenwriter Diablo Cody recently discovered it), problems remain: Only its Japanese edition displays advertisements, and executives still haven't unveiled any alternate revenue stream. And despite a recent employee shuffle on the engineering side, the service is still plagued by outages that, while certainly not any kind of global catastrophe, can be quite a bit annoying for active users.