If you thought apps were just a passing fad, think again. Research firm Gartner today published a report projecting mobile application stores to generate revenue of $15 billion this year alone, with global app downloads topping out at 17.7 billion downloads in 2011.

If realized, 17.7 billion app downloads would represent a 117 percent increase from an estimated 8.2 billion downloads in 2010, according to Gartner. By the end of 2014, Gartner forecasts over 185 billion applications will have been downloaded from mobile app stores since the launch of the first one in July 2008.

“Many are wondering if the app frenzy we have been witnessing is just a fashion, and, like many others, it shall pass. We do not think so,” said Stephanie Baghdassarian, research director at Gartner, in a press release.

Baghdassarian believes that apps represent a significant opportunity but adds that they will have to “grow up” and “deliver a superior experience to the one that a Web-based app will be able to deliver.”

Gartner analysts said the hype around application stores in 2009 continued through 2010 with alternative offerings to the Apple App Store gaining some traction. Android Market, Nokia’s Ovi Store, Research In Motion’s (RIM’s) App World, Microsoft Marketplace and Samsung Apps are the key competitors that saw the number of application downloads grow in 2010.

Baghdassarian puts an emphasis on the influence Apple’s App Store has had on the space. Gartner estimates that Apple’s App Store drove close to nine application downloads out of 10 in 2010 and will remain the single best-selling store across the company’s forecast period (through 2014), although to a lesser extent as other stores manage to gain momentum.

“Application stores have become a highly visible and potentially lucrative part of the smartphone ecosystem, largely due to Apple’s App Store,” Baghdassarian says.