1. Do you click on the link in the results page?
2. After clicking on that link, do you go back to the search or not?
3. How long do you stay there before coming back?
Adding an explicit up/downvote would capture some additional information, but it would overlap with the above, and most users would ignore the button. I’d guess Google has at some point experimented with this and found it wasn’t worth keeping.
1. Clicking on a link is often a negative signal. If you're searching for "when was barack obama born?", hopefully you get the answer on the search results page itself, so you never have to click. Or, the caption for each search result should have a snippet containing the answer.
2. If you stay a long time on the search result you click on, is it because the information is hard to find or because the page is deep and useful?
I used to work on Search measurement at YouTube and Facebook, and run a human evaluation platform now. Here's an example what they can look like when you use high-quality raters: https://demos.surgehq.ai/google-vs-bing/
Sounds pretty ripe for abuse too.
civilized wrote (emphasis by me): "and Google enhances its ranking for me based on that".
I love stackoverflow content, but hate the surface, e.g. how it loads jquery from google (???) and if I disable it, then the content breaks, because obviously the only way to implement a toggleable div is when you send your users browsing history to google directly..
I would suggest that the big reason not to go down the avenue of social buttons is the inevitable gamification of it. Already we have have ratings farms for apps and amazon. Of course we will have similar if search implemented this.