If you’ve got one of the popular Tap Tap Revenge games installed on your iPhone or iPod touch, you’re not alone.

Developer Tapulous says its App Store sales have approached $1 million per month, according to a report from Reuters. The developer is another sign that Apple’s devices and its often-controversial App Store are fertile ground for start-ups, even in an otherwise weak economy.

Tapulous’ Tap Tap Revenge game series has been installed more than 20 million times, with more than 600 million total games played. Earlier this year, research firm comScore reported that the game had been installed by a full 1/3 of Apple app users.

Not bad for a company with a mere 20 employees, although Tapulous isn’t revealing precise sales data -- only that they are indeed profitable. The company’s profits come from several diverse methods, including charging for certain games, through ads in others and also selling songs within the games themselves. Tapulous initially raised $2.8 million from investors, including Salesforce.com CEO Marc Benioff and venture capital firm Khosla Ventures.

CEO Bart Decrem predicts a wave of huge growth in mobile app commerce over the next two years, citing other successes from Zynga, Playdom and Playfish, the latter of which was recently acquired by Electronic Arts for $275 million in cash.

“It’s going to be big and all of a sudden people are going to say, ‘Holy cow, where did those guys come from?’” remarks Decrem.