That was fast: OS X Mountain Lion running on 1 of every 10 Macs

Based on web traffic data, it appears that ten percent of all Macs accessing the web have OS X Mountain Lion installed, just one month after the desktop software’s release. That’s a really fast uptake for a desktop OS upgrade, especially for Apple(s AAPL), according to data compiled by Chitika Insights.

Chitika derives its data from sampling “hundreds of millions” of desktop web ad impressions and the operating systems of the computers that access these ads.

Apple unveiled the latest version of OS X on July 24 and only made it available via download from the Mac App Store. It also slapped a $20 price tag on it, $10 cheaper than the previous version of the software, OS X Lion. By comparison, Lion took three months to reach a 14 percent base installation, according to Chitika.

One in 10 is nothing compared to how fast Apple’s mobile software is updated by its users. For example, a month after iOS 5 was released in October last year, it was on approximately one out of every three iPhones and iPads. But iOS updates are free. Desktops have not traditionally seen quick uptake rates like that, and the speed of Mountain Lion’s adoption is unprecedented for Apple desktop software, it’s safe to say. Here’s Chitika’s tracking of the installation rates over this last month:

The spike seen in our previous Mountain Lion study actually continued past the first 48 hours, plateauing at 5.65% on July 29th, a full four days post release. Mountain Lion users represented an average of 9.61% of all Mac OS X traffic from August 20th through August 27th, and the adoption rate has shown no signs of letting up. By August 27th, Mountain Lion usage constituted 10.3% of all Mac-based desktop impressions seen over the extensive Chitika ad network.

The initial release was well-reviewed, but it wasn’t perfect; Apple released its first major update to Mountain Lion to squash some of the reported bugs last week.