Japanese e-commerce giant Rakuten has confirmed it is leading a $100 million investment in Pinterest, together with existing backers Andreessen Horowitz, Bessemer Venture Partners and FirstMark Capital plus angels.

WSJ reports sources as saying the deal means a $1.5 billion valuation.

Rakuten CEO Hiroshi Mikitani (via announcement):

“While some may see e-commerce as a straightforward vending machine-like experience, we believe it is a living process where both retailers and consumers can communicate, discover, and curate to make the experience more entertaining.

“We see tremendous synergies between Pinterest’s vision and Rakuten’s model for e-commerce. Rakuten looks forward to introducing Pinterest to the Japanese market as well as other markets around the world.”

In other words, Rakuten is excited about how enthusiastically Pinterest users clip and share items they might want to buy.

Pinterest CEO Ben Silberman:

“Our goal is to help people discover things they love, by connecting people through their shared interests. Bringing Rakuten on board gives us an amazing opportunity to move a step closer to this goal.”

Pinterest’s visual presentation of those products is not the only potential boon to e-tailers (it wouldn’t take a rocket scientist to present product listings in this way); the tie-in with social sharing could effectively enable social commerce.

There is a wide number of retailers for which Pinterest could perform this role:

• Rakuten has built up its heft through acquiring the online retailers Buy.com in the U.S., Priceminister in France, Ikeda in Brazil, Tradoria in Germany and, recently, Play.com in the UK.
• It also recently bought the Kobo e-reader and e-book store business.
• And it has made investments in Russia’s Ozon.ru and the AHA Life luxury shopping site.

Pinterest has boosted web referrals for sites in certain categories like women’s lifestyle publishing, so some publishers, as well as retailers, had become excited about the possibilities.

It’s unclear what the e-commerce investment means for the media’s current Pinterest penchant, but some pundits think content and commerce is a marriage made in heaven.

The Next Web had reported on Wednesday its expectation that Pinterest would announce a funding round at a $1 billion valuation on Friday, which is also Facebook’s IPO day.

Pinterest had previously taken a total $37.5 million from angels, Bessemer, Ron Conway, FirstMark, Andreeson Horrowtiz and others, through an angel and two proper rounds.

The title is a riff on “FMOT,” or “First Moment of Truth,” a term Procter & Gamble coined years ago to describe a shopper’s first interaction with a product on the shelf. For the book, Google (NSDQ: GOOG) worked with IPG Mediabrands’ Shopper Sciences to conduct a national study on how digital media is changing shopping behavior.

The study showed that 84 percent of the over 5,000 respondents engaged in pre-shopping activities, such as internet research or comparison shopping online, ahead of their retail store visit. “Our research confirms a growing trend of digital pre-shopping activity that is both informing and directing shopper choice, regardless of whether the purchase is ultimately made online or in a retail store front,” said John Ross, CEO of Shopper Sciences.

Jim Lecinski, the book’s author and Google’s “chief ZMOT evangelist,” told paidContent he was most surprised by the fact that the online research typically associated with “higher-ticket, higher-involvement” items like cars and flat-screen TVs has spread to everyday products like cough syrup, gum and mascara. “It was surprising to us that shoppers will [go through the online research process] for gum,” he said. It’s a process they’ve learned from researching “the $40,000 SUV.”

The study found that shoppers are using, on average, 10.7 different sources in their decision-making process and they are increasingly relying on internet search, retailer and manufacturer websites and social media to become more informed about products. “Marketers often fail to register the influences behind seemingly impulsive decisions because standard methods for measuring marketing ROI don’t factor in all of the influence nodes shoppers are actually using in their decision-making process,” Ross said.

Lecinski recommends that companies type their product, category, and brand name into their search engine “of choice” followed by the word “reviews” or “ratings” or preceded by the word “best.” “Increasingly, this is where consumers are making their buying decisions,” he said. “The average household income in the U.S. is somewhere around $56,000. Cough syrup is $10. If you buy the wrong cough syrup and have to go spend another $10 out of the tight recession household budget–as one mom told us, ‘Now I can’t give my kids dessert in the last week of the month.’”

We mentioned Consmr, a new site aiming to be a “Yelp”-like review hub for consumer products. “That’s definitely in the spirit of ZMOT,” Lecinski said. “It’s recognizing that consumers now expect to do this [research].”

Other findings from the study, and contained in the e-book:

–79 percent of consumers say they use a smartphone to help with shopping.

–83 percent of moms said they did online research after seeing a TV commercial that interested them.

–70 percent look at product reviews before making a purchase. In the book, though, Lecinski advises marketers to “relax” about product reviews–they tend to be good (as the Amazon top reviewer survey we posted about last week also suggested):

“We’ve found that the worldwide average for product reviews is a 4.3 out of 5.0,” says Brett Hurt of Bazaarvoice. His company provides customer conversation services to corporations ranging from Wal-Mart (NYSE: WMT) to Johnson & Johnson. According to Brett, 80% of all reviews online are four to five stars.

–Shoppers’ top online social activities were: Getting an online referral from a friend; becoming a friend or follower of a brand; reading blogs where the product was discussed; and seeing the brand mentioned on a social networking site like Facebook.

Winning the Zero Moment of Truth is free as an e-book. Google also partnered with Vook to create a free enhanced e-book, including video interviews with execs from companies like Johnson & Johnson and General Electric (NYSE: GE). Both versions are here.