I noticed this morning that when you search for something on Google, then click on the listing, and click "Back" button on your browser. There is "Was this link useful?" below the Title of the page and there are "Yes"/"No" button next to it.

Let's see if this "Yes"/"No" vote affects the organic rankings on Googlee.... It would be another click fraud issue coming up on the organic side in the near future......

You're seeing a UI test that is not available universally to all Google searchers.

As for how the data would be used, give Google credit for being smart enough to know that a simple feedback Q&A like that would be incredibly easy to spam/fake.