I have to agree with futtta. There is nothing on the WordPress.com Stats download page even mentioning third party tracking in addition to the fact that Quantcast is being added to a lot of anti-tracking lists and would be unreliable.
I installed WordPress.com Stats from the beginning because I liked the simplicity of it. Now, its the only script on my site that needs to load synchronously because of the use of document.write. I have ran many tests and the WordPress.com Stats (combined with Quantcast) take longer than the rest of my page to load.
In addition, I also installed WordPress.com stats because it did not set any cookies whatsoever. Now with Quantcast, it sets a cookie under my domain name as well as their own quantserve.com which is detected by most anti-malware products as a 3rd party tracking cookie.
I want to continue using WordPress.com Stats but lately some unnecessary features have been added including the wp.me shortlink which I don’t need as I have my own shortlinks.
I would love to see a “lite” version as well with just the basic Stats like it used to be without any of the other stuff. I don’t need a unique visitors feature with WordPress.com Stats. I have Google Analytics and CloudFlare to do that (both of which don’t use unnecessary third party services).