Branding you just can't buy.

The big news out of Silicon Alley yesterday was the big $40 million round raised by Fab, a start which pivoted its business model less than a year ago and has now scored a $200 million valuation led by Andreessen Horowitz.

What drove Fab's sudden success? It's got a seasoned leader in Jason Goldberg. Flash sales are a big opportunity when executed right. The company builds its own technology.  But according to folks in the know, a lot of the credit goes to Ashton Kutcher, who holds a much larger stake in the company than has been reported.

How to put a value on what Mr. Kutcher brings to the table? Fab tried in a blog post, noting that a single tweet from Ashton drove nearly 6,000 sign ups to their site. Extrapolate that across the numerous times Mr. Kutcher has tweeted about Fab and Mr. Goldberg and you can forget about the cold start /ghost town problem that most startups are faced with.

If you were to try and put a monetary value on that marketing/customer acquisition, you could compare it to the cost per tweet for celebrities that get paid to endorse products through services like Ad.ly and Izea. According to this story from MSNBC, a tweet from Lindsey Lohan clocks in at $3,500 and Mr. Kutcher has about three time more followers, each one of Ashton's tweets linking back to Fab has a market value of roughly $10,500.

It's a nice chunk of change, though it pales in comparison to the six figures a startup would have to drop in order to get a full page spread in Details magazine or the millions some quality airtime on Two and Half Men might cost, given its one of the most popular comedies on primetime.

Take it from Fab CEO Jason Goldberg, "It must be noted that outside of this one little experiment, Ashton Kutcher has driven tens of thousands of new Fab.com membership that have resulted in thousands and thousands of sales."

To put that in context, we'll turn to our pal Courtney Boyd Meyers from the Next Web. "It took Facebook 10 months to reach 1 million members and took Twitter 24 months to reach 1 million members. Meanwhile it took e-commerce competitor One King’s Lane 26 months to reach 1 million members."

Disclosure.