Much has been made of the rebirth of consumer hardware startups. But some high-profile examples have stumbled out of the gate.

FORTUNE -- To hear some in Silicon Valley tell it, hardware is the new software. In other words, after years of taking a backseat to the splashy launches of countless websites, apps, and the cloud, innovation on the hardware side is ramping up again. Is it? Several high-profile launches have stumbled. Here are three examples that prove how hard hardware really is.

Exhibit A: The Jawbone UP
When Jawbone, the San Francisco-based purveyor of wireless devices, originally launched its head-turning, movement-sensing wristband in 2011, the company found itself in the middle of a firestorm. Put simply, users complained that the device didn't work. (Anecdotally, every 3 out of 5 users I spoke to in the device's early days complained to me about the problem.) The outcry was so widespread, Jawbone recalled the product just a month after, offered refunds, and relaunched a redesigned version late last year. Certainly that was a smart move on Jawbone's part, but for UP, it's fair to say the damage has been done.

Exhibit B: Pebble
When we wrote about Pebble last month, we said that the next wave of hardware -- wearable computing -- was already here, Google (GOOG) Project Glass and Apple (AAPL) iWatch be damned. While the firm's 11 full-time employees have shipped over 75,000 watches to date, reviews call the device a great concept that needs improvement. Some argue the display could be sharper, the standard watch band less cheap-feeling. App selection remains limited, and the watch has proven to have some connection issues, at least with iOS devices. To be fair, the company's main goal this year is to help developers create better software features for the Pebble, but skeptics remain. "What Pebble has done is captured tremendous excitement from developers and early tech adopters," says Sarah Rotman Epps, a Forrester analyst, who argues that isn't indicative of broader mass-market success. "It doesn't have all the fuctionality yet of something one would expect to be an extension of your smartphone."

MORE: 8 PCs that want to bring sexy back

Exhibit C: Ouya
The $99 home video game console spearheaded by game industry vet Julie Uhrman generated tons of buzz when it was announced last July. The idea: create a video game console for people who don't want to shell out hundreds and employ an accessible, Android-based open-source development environment so even frugal grassroots coders could put out a game. While the official consumer release isn't until June, units have already begun shipping to Kickstarter backers, and early reviews haven't been so kind. "The controller needs work, the interface is a mess, and have I mentioned there's really nothing to do with the thing?" wrote The Verge, which gave the console a mediocre 3.5 out of 10 rating. Ouya shot back, stating the pre-release hardware being sent out was just that -- pre-release -- and Uhrman clarified in a separate blog post that things like  convoluted game install processes will be fixed come summer, but it's clear the startup has a lot of work to do between now and then.

This isn't to say there won't be a hardware "reawakening," of course. Plenty of companies like Pebble and Ouya are working on hardware that could ultimately prove revolutionary. But the "hardware renaissance" has some way to go yet.

What do you think, Fortune readers? Chime in with comments below.