The most highly funded project in Kickstarter history is starting to feel some serious heat from backers.

Eric Migicovsky's smartwatch maker Pebble raised more than $10 million earlier this year by treating its investors like customers--if you supported the project, you'd get a watch.

But now, it turns out, those backers expect to be treated like customers--and some are getting tired of waiting for the product they "ordered."

The trouble began in July. After months of promising that the smartwatches would come out in September, the company announced it no longer had a shipment date. Pebble added that it would "soon" be manufacturing 15,000 Pebbles a week out of a factory in Taipei, Taiwan.

Now September has come, and backers are unhappy that there is still no firm date.

"It's obnoxious," says Joshua Hernandez, an early Pebble backer. "If they don't announce [a ship date] within the next two weeks, I'm done. I'll go get one of the Android versions of this, or the Sony version. It's just too long to have something on layaway." Hernandez says he put $200 into the project in April. 

In addition, some backers recently took to the project's Kickstarter page to vent: "OK, you don't know when you'll be able to start shipping but do you already know you won't ship before November?" one commenter wrote.

Erica Shaffer, a representative for Pebble, told Inc. the company is "close" to shipping.

Unfortunately, Pebble's 85,000 backers who prepaid for a Pebble have no legal recourse to receive a refund. "I don't know where I could go and cancel [my order]," Hernandez says. "It's not clear to me that I can even do that."

Recently, several Kickstarter projects have faced a backlash after failing to deliver on promises after reaching their funding goals. Entrepreneurs are finding that the alternate funding strategy may be a double-edged sword.