Why is this man smiling?

Is Twitter really worth $1 billion? Some investors apparently think so, with TechCrunch reporting that the fast-growing microblogging service will soon close a new venture round of $50 million or so at a whopping $1 billion valuation.

No new investors have yet to be named. But if the $1 billion figure is accurate, one Seattle area billionaire -- known for a big laugh -- should be smiling even more right now.

Amazon.com founder Jeff Bezos invested in Twitter last year when its valuation certainly was nowhere near the $1 billion mark.

[Post updated with report from TechCrunch that Insight Venture Partners is leading the new round]

In fact, GigaOm placed the pre-money valuation at about $80 million at the time of the $15 million round.

Twitter raised another $35 million round from Benchmark Capital and others earlier this year.

Nonetheless, going from $80 million to $1 billion is an absolutely crazy increase in valuation in a little more than a year.

But I guess that's what happens when your Web service tops 50 million visitors. Twitter is still losing piles of money, and has yet to turn on any sort of real revenue engine.

But I am sure that Bezos and the other early investors -- including many employees -- are likely to be feeling pretty good about things. But, of course, that investment will only be realized when Twitter sells out or goes public.

That's part of why it will be interesting to see who emerges as the backer of Twitter at the new valuation.

Microsoft already placed a huge $240 million bet in the social media arena on Facebook, at the time giving the Silicon Valley upstart a $15 billion valuation. Could it put its tentacles into Twitter as well?

Google, Amazon, Apple, News Corp., IAC and others have all been tossed around as possible acquirers of Twitter. Maybe one of them will want to get a place at the Twitter table in this round.

UPDATE: TechCrunch -- citing an unnamed source -- reports that New York-based Insight Venture Partners is the new investor in Twitter and notes that even more money might come in.