Last week Google acquired popular email client Sparrow, and the reactions have been mixed — many users are disappointed that their favourite app won't be getting new features, while others are simply sad that the Sparrow team won't get to work on the projects they want to. A number of notable app developers have weighed in as well, and their reactions make it pretty clear that even with a successful app like Sparrow, building a sustainable development business isn't easy.

"Sparrow did everything right," wrote David Barnard, founder of App Cubby, the team behind Launch Center Pro. "They built an incredible email app with broad appeal and released it into the hottest software market the world has ever seen. And yet it was a financial flop." One of the problems, he says, is the current pricing model, where users expect "more and more value from software while paying less and less for it."

While Sparrow sold well, without any kind of revenue stream outside of the initial purchase, it appears that it simply wasn't enough to keep the business going. "The age of selling software to users at a fixed, one-time price is coming to an end," said Barnard.

Instapaper's Marco Arment, meanwhile, says that he's received similar offers to sell, but never moved forward because he didn't want his app to be shut down. "I was only able to reject those offers because Instapaper is a healthy business," he explained, though in a follow-up post he added that "In the reality of our fast-paced, boom-and-bust industry, even very strong support from customers may not be enough for many companies to stay in business."

That appears to be the case with Sparrow. So while many users were quite upset at the news — since it meant that, for instance, we won't be seeing the long-awaited iPad app — it seems that it was the best business decision for the team. And while that's disappointing, it's hard to fault them for their choice.

"The Sparrow guys have homes, and families," wrote developer Matt Gemmell. "They have every right to cash out and take new jobs. They're winners."