That was a bit scary... I started responding to a question on StackOverflow, but then decided to switch to another machine and respond from there instead. I opened StackOverflow in the browser on the other machine, searched up the question I was going to answer, and lo! The text I'd typed in the other browser on the other machine
was already there!
I knew StackOverflow tries to be helpful by caching what you type in local storage, but this clearly shows that they also cache it server side. This is the infamous 'we know what you type even if you don't send it' creepiness that even Facebook has been critisized for. With facebook you would expect such creepiness, but I did not expect if from StackOverflow...