After receiving a $100 million investment from Japanese e-commerce site Rakuten, the "next Facebook," got a valuation 50 percent bigger than the already unbelievable price of Instagram. Meanwhile Facebook still needs to convince advertisers and investors that it's worth as much as it is as readies itself to IPO tomorrow. Facebook at least has a business model. Pinterest, admittedly, does not. Hear that bubble?

Before this round of funding, Pinterest was just hoping its popularity would turn into profits. It had a kind of a money from magic mentality. "My hope is that if we build a service that a lot of people use to plan and discover things, that will be really valuable," Pinterest CEO Ben Silberman told the Wall Street Journal back in February. It had some vague ideas for how to make real dollars back then, but since the company has yet to implement anything. This latest round of funding put money toward this still moneyless company.

But, Pinterest does have some hope beyond Internet advertising -- that ill-fated money-maker, which is now failing Facebook and brought the demise of the dot-com bubble. The social network thinks it can tap the Internet shopping market. "The traffic coming from Pinterest probably will have a very high conversion rate," Hiroshi Mikitani, chief executive of Rakuten, told the Financial Times's Tim Bradshaw, justifying his investment. Yet, he doesn't sound too convicing, using a lot of qualifiers, like that word "probably" up there. Or when asked if "social discovery" could ever drive shopping, Mikitani reponded: "We don’t know. It’s too early to tell." This all sounds very murky, right?

Bubbles, as we learned from The New York Times, happen when "mania causes the price of an asset to soar far above its intrinsic worth," as the Times's James B Worth put it. One billion dollars sounded like an overvaluation for a smartphone photo app that makes absolutely no money, when Facebook purchased Instagram. One and a half billion sounds similarly absurd, considering Pinterest, too has not proven it can make money. And as Facebook's IPO shows, even the king the new Internet hasn't proven itself. GM just pulled its $10 million ad campaign. That move, while not a blow to Facebook's $3.7 billion dollars yearly revenue, has the rest of Madison Avenue worried. "My colleagues and I have spoken with several other advertisers who were already thinking of putting their dollars elsewhere," Melissa Parrish, an analyst at Forrester told DealBook's Tanzina Vega, Evelyn Rusli and Peter Eavis. "Now that G.M. has done so in such a large and public way, many of the fence-sitters will know that they’re not alone," she continued. Bad sign.

And it's not just this coming advertising implosion that stinks bubble. We're seeing that deadly Silicon Valley hubris. "We're the best thing happening in America," a tech entrepreneur told the Los Angeles Times's Jessica Guynn, who describes all the crazy spending happening in the Bay Area. "[Celebrities] might be more famous, but this is where the true value is being created." True value is an overstatement. (See above.) And, these guys are spending their Facebook IPO money even before it's cashed out. "Others are spending in advance of their big payday, fueling an economy that's already humming thanks to the Bay Area's thriving technology sector," continues Guynn.

But Pinterest's investors are not worried. "Pinterest is a little bit different from Facebook," continued Mikitani. This is true. Unlike Facebook, Pinterest can't even pretend to create value, in the dollars and cents sense.