"It can be very difficult to do that when you are out there raising money with the vision and the big excitement and a long-term view of things," Lipsky says. "It's a managerial issue. Building a culture of focus is just as important as a culture of hard work, working long hours and hiring smart people."

He admits that it sounds counterintuitive, but start-ups also need to be agile and willing to commit to strategic shifts in either product or service.

A killer mistake is when entrepreneurs don't focus sufficiently on customers and their experience with a product. In many cases, a launch can be rushed.

"Many entrepreneurs get excited about being first to market," Lipsky says. "It's very exciting because you are inventing something and thinking that because you are first to market you are going to succeed. The problem is that you are in the difficult position of educating the market about what the product is and why the market needs the product. You are also making product and service mistakes for the first time. It might be ideal to be second or third to the market. After the market is validated, then you can learn from the mistakes that have already been made."

Buzz may help draw in investors, but hype alone doesn't guarantee a company's success.

Pownce was a social media/microblogging site launched in 2007. The involvement of co-founder Kevin Rose (an entrepreneur associated with Digg, Revision3 and TechTV) gave the service instant, favorable media coverage that heralded it as the hottest of hot Silicon Valley start-ups. Advance sign-up invites were snatched up on eBay ( EBAY).

Once all that frenzy subsided, the verdict was a resounding "meh." The site never lived up to the hype and couldn't capture, or retain, the dedicated user base it needed for survival.

By Dec. 1, 2008, less than a year after the public was allowed to log on, it was announced that Pownce was joining forces with blogging software company Six Apart. Despite promises of a new, improved site in 2009, Pownce never returned.

There were also high expectations for Quora, an online community where members shared their expertise via questions and answers. Founded in 2010 by former Facebook executives, the company was valued at roughly $1 billion lat year.

Quora is alive and well, though certainly not uttered in the same breath as Facebook or Twitter these days. In fact, even Quora has fielded the question, "Is Quora overhyped?"

For a very brief time, Chatroulette, created by a 17-year-old from Moscow, looked like it was going to be the next big thing in social media. The service -- which pairs Web-chatting users from all over the world anonymously -- failed to make it big with either investors or advertisers. As anyone who has ever visited the site can attest, adding anonymity to webcams equals nonstop genital exposure. Several comprehensive efforts to clean up the site have been tried, and failed, since the 2009 launch.

The following is a look at some other heavily hyped tech start-ups that never lived up to expectations and reside in the "Where are they Now" file:

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