It has only been out for two days, but OS X Mavericks already accounts for 5.5% of OS X’s total web traffic in North America, according to tracking firm Chitika. For comparison, Mountain Lion adoption was only at 1.6% two days after its release next year. It took four days for Mountain Lion to reach Mavericks’ current adoption rate, so we’re looking at double the amount of people upgrading within the first week.
Mavericks’ success is probably tied to the fact that Apple has made it available for completely free. We should have more exact Mavericks numbers from Apple after its upcoming earnings call.