Apple unleashed OS X Mountain Lion just last Wednesday, but it’s already on 3% of compatible, web-browsing Macs, according to numbers that the web tracking firm Chitika provided to AllThingsD. The quick adoption is likely due to the low price that Apple is charging: Mountain Lion costs just $20 on the Mac App Store and is just a download away, making the operating system easily (but not necessarily quickly) attainable for users with a broadband internet connection.

According to Chitika:

“Moreover, based on Apple’s June 2012 announcement that there are currently 66 million Mac users in the wild, we can infer that 2.11 million Mac users downloaded OS X Mountain Lion in the past 48 hours. Using this figure, if we assume that 90 percent of these users paid to upgrade, OS X Mountain Lion generated $38 million in revenue for Apple in the past 48 hours.”

If Chitika’s numbers are correct, 2.11 million Macs are currently running OS X 10.8. Those are some pretty great numbers, and they’ll only continue to grow throughout the next few months. As I’ve been using Mountain Lion, I can definitely say that those who are waiting have no reason to: Mountain Lion is a fantastic operating system.

Microsoft is also going to be releasing Windows 8 at a lower price than normal, following in Apple’s footsteps. Apple started its low operating system pricing scheme with 2009’s release of 10.6 Snow Leopard for $30, followed by the $30 Lion in 2011, and finally Mountain Lion this year for just $20. Based on the high adoption rate for Macs because of the low prices, I expect adoption numbers for Windows 8 to be very similar.

If you own a Mac, have you upgraded to Mountain Lion yet?