Apple has announced that Mountain Lion is the most successful OS X release ever. In the first four days of availability on the Mac App Store, OS X 10.8 Mountain Lion was downloaded more than 3 million times.

“Just a year after the incredibly successful introduction of Lion, customers have downloaded Mountain Lion over three million times in just four days, making it our most successful release ever,” said Philip Schiller, Apple’s senior vice president of Worldwide Marketing said in a released statement today.

We'd guess that both the low $20 price and the ease of updating thanks to the Mac App Store contributed to the early success. Have you upgraded yet? If you're still on the fence, check out the 10 features that make Mountain Lion a steal. You can get Mountain Lion now on the Mac App Store.