Analytics firm Chitika on Tuesday revealed the findings of a recent study that shows the latest Blackberry PlayBook operating system update is already running on 43.7% of devices after just one week. “It would seem that this rapid rate of adoption is expected given that the upgrade was free and in many cases automatic,” Chitika said in its report. “If the use of the OS continues to grow at this rate with 50% decay, market majority will be achieved in two weeks, and by three weeks 75% of all PlayBook OS eligible devices will be running the upgrade.” The highly anticipated update to Research In Motion’s struggling tablet brought a number of much needed improvements to the PlayBook. Perhaps the most important additions were native email, contacts and calendar functionality, while BlackBerry Messenger support is still nowhere in site. After the update, PlayBooks also benefited from the addition of RIM’s Android app player, which allows repackaged Android applications to run on RIM’s tablet. Read on for Chitika’s press release.