As I wrote in my Scientific American column this month, crowdfunding sites such as Kickstarter and Indiegogo are rapidly changing the way new products are born. These sites let inventors appeal directly to the public for money to develop their creations and bring them to market—quickly and without any corporate meddling.

Some truly great products have reached, or are on their way to, the public via these sites, including the Pebble smartwatch and the Coolest picnic cooler (that has integrated speakers, blender and phone recharger).

About 41 percent of Kickstarter campaigns reach their fund-raising goals; about 10 percent of Indiegogo campaigns succeed. The rest disappear, and people who pledged to support those failed campaigns are never charged.* The most obvious cause of crowdsourcing failure is not having a good enough idea. One tragic/hilarious list highlights 37 of the absolute worst Kickstarter failures: They include a handmade bag for picking up guinea pigs from their cages (total raised: $0); a service to deliver year-round mail from Santa (raised: $0); and “HouseBoy: A Frisky Gay Board Game” (raised: $5).

But the thing is, when you contribute to a crowdsourcing campaign, you have no guarantee of anything—that the product will reach its goal, that a successfully funded project will actually become a product or even that the project is real. Very, very few turn out to be products that don’t exist at all—or fail to be the product they promised to be. Herewith are three high-profile crowdsourcing efforts that didn’t deliver:

Eyez: These high-tech glasses were supposed to record what you see in your life and post it to Facebook. It raised $343,415 on Kickstarter in 2011. Backers who offered at least $150 were supposed to receive a pair of these glasses by the end of 2011. They have yet to materialize, although public relations folks from the company have blamed delays in production and say that those who pre-ordered pairs have been refunded.

GoBe: This was a calorie-counting wristband whose creators sought $10,000—and raised over $1 million. But scientists and doctors dispute that calorie intake can be measured through your skin, and the creators haven’t convinced many people that the thing actually works. One Web reporter has hounded them for months and received only hedging and double-talk. Those behind the campaign have shown off rough prototypes but insist that manufacturing delays and U.S. testing are holding back shipment of the devices. In the meantime, they have back-pedaled on some of the claims originally listed in the initial pitch. The ship date as of this writing is this September.

Kreyos: This was supposed to be a waterproof, voice-activated smartwatch; it raised $1.5 million on Indiegogo. After repeated delays the company finally shipped a watch—but not the one it had originally advertised. The finished product lacked voice and gesture controls for sending messages and e-mails, making calls and so on; came without support for Siri and Google Now; is waterproof only to a depth of one meter, not five; and, at this writing, still lacks apps for communicating with your phone.

The vice president of the company has since resigned. But the frustration of Kreyos backers wasn't helped when a photo of its creator popped up on Facebook—posed with a new Ferrari.

*Clarification (9/17/14): This sentence was edited after posting to more precisely describe how contributors to failed campaigns retrieve their donations.