I just read this Electronics SE answer. I found the explanation very clear and interesting, but I don't want to create an account on that site. So, I clicked Yes by "Was this post useful to you?"
Who will get that feedback?
Some statistics are available to 10k users in the tools section, via http://stackoverflow.com/tools/post-feedback
These pages shows some general statistics on the feedback (like feedback/score correlation), and there are tabs that list the most over/under-rated posts, as well as the most and least helpful posts.
Moderators probably have finer-grained information, and obviously Stack Exchange staff more so.
Looks like this on Stack Overflow:
The 10k tools page is dead for some time now (over a year) however the team added the PostFeedback table to the public data dump, accessible for example via data explorer.
Quick count of rows showing over 13 millions records at this time.
Another interesting query is Anonymous feedback votes over time, showing steady increase in votes:
(last month doesn't really count as it's not yet finished)
The feedback is recorded in a page that is visible to 10k users and moderators on http://electronics.stackexchange.com/tools/post-feedback, in the case of the site you are referring.
The page reports some statistics about the anonymous feedback, and makes a comparison between anonymous feedback, and the votes given to the same posts.
This is how the top of that page appears on English Language & Usage.
The same information is visible to moderators, who don't get more data. This is what I see on Drupal Answers, where I am a moderator.
Even the rest of the page is not different, if I compare what I see in a site where I am a 20K user with what I see on Drupal Answers, I don't see any difference.