So I actually worked at cognitive networks up until the end of 2014. I've read this thread and thought I would address some things here that didn't seem to get fully concrete answers (in no particular order).
The ACR technology that cognitive used was/is in vizio and LG tvs. during the time I worked there we only had a deal to use it actively on vizio tvs. I guess lg was just testing the waters to see how it'd work. The ACR technology that CG used is based on RGB values from sampled patches on regions of the image. There was no audio finger printing used. There were a number of items that would mess up the "recognition". Some of those included aspect ratio of content, watermarks from different providers, overlays and basically anything that modified either the size of the original image or obstructed it. For the server infrastructure, what we did was we ingested live feeds from the major network providers, these feeds had to be ahead of what tvs were watching by at least 5-10 seconds so we actually had the fingerprint data in our database to be recognized. we would pair the ingested fingerprints to TV scheduling data and voila, we "knew" what you were watching. Now clearly if we didn't have the content in our database we had no idea what was being shown on your screen.
What did we use the ACR data for. Well there were 2 "deals" going on while I was there. One was ratings, something to compete with the likes of neilsons. Different content providers, distributors, marketing agencies, etc. would want ratings info. Additional there were other "data mining" companies that build profiles based off public IP addresses that would want to use our data to enhance and augment their data. The other application that was the one that everybody was after want "interactive advertising". This would allow us to pop up an HTML5 app/page based on the ACR. So for example your selling a car, your ad comes up, you pop up your app and allow the user to schedule a test drive or look at the car in more detail. The use cases were endless though.
The ACR technology ONLY worked on content that was viewed from the HDMI ports. Any built in apps like netflix or hulu that were run, ACR was force disabled. One thing I remember about that was that netflix is huge about NOBODY getting viewing data/ratings information about netflix and it's users. Only netflix has that data apparently. One somewhat reassuring thing about disabling the technology is at one point vizio did notice a bug on one of its TVs where ACR was not being disabled when the user opted out of "interactivity". This was a big deal and we were required to solve it ASAP.
AMA if I missed something.