There was plenty of that with the first .com implosion. Many e-commerce sites actually did have customers (eg. my sister swore by Kozmo.com), it's just that they got them by selling goods for less than they paid for them, and then the customer base dried up once they had to actually make a profit.
The big scam now is in customer acquisition: companies spend more in marketing than the LTV of a customer and make up the difference with VC cash. This is a little bit easier to hide: you have positive gross margins, explosive revenue growth, and the appearance of a sustainable business, but once you take your foot off the gas and stop spending VC money your existing customers churn away and you can't acquire new ones. Google and Facebook are also making out like bandits from this, and may get hurt significantly when the bubble bursts.