Mayer now has a team that works the way she wants to work, the way she knows Yahoo! has to work. And she can demonstrate that work style to the men and women who will decide whether Yahoo!'s media ambitions, and its advertising ambitions, have traction.

As Tumblr becomes Yahoo! East, Mayer can turn her head toward Alibaba, the Chinese e-commerce supermarket that still needs a U.S. home, with renewed confidence. Yahoo! still owns 20% of Alibaba. If the Tumblr style can get into the marrow of Yahoo programmers, Mayer may be able to build the bridge to crack the retail market on Chinese goods wide open.

I know. "Having just the vision's no solution, Everything depends on execution." (Stephen Sondheim, a New Yorker.) But, with Tumblr, no other tech company has as many of the moving parts needed to build an immense cloud-based product-and-services ecosystem as Yahoo!. Google lacks the product connection, Facebook lacks the New York base, and Amazon.com ( AMZN) lacks the sizzle that comes from having both the Valley and the City, under one virtual roof.

I don't think Tumblr was worth $1.1 billion to anyone else. I think, in the end, Mayer knew she was bidding against herself, and was swooping in with a blow-them-away offer. She has to keep that Tumblr team together, and that Tumblr style, which will be tough once the money comes raining down on people who have never seen it before.

She's depending on her own skills, as a development manager, as an executive, and (yes) as a celebrity to make it happen. It's a huge risk. But that's what good business stories are made of.

At the time of publication, the author was long GOOG and YHOO.

This article is commentary by an independent contributor, separate from TheStreet's regular news coverage.

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