Seems they're part of a trial "Edit Results" program Google is testing on a random selection of people with Google Accounts over a few weeks. They set up an informational page to explain it more. This feature only applies to people who are logged in to their account when searching, and it only affects the result list of that particular user.
You can click on the Up arrow to promote good results to the top, delete bad ones altogether, and add notes about different results.
This seems like an interesting way to approach user-feedback-driven search, without actually making Google search results user-feedback-driven. However, if they could figure out a more configurable way to do this (split into different "Search Sessions," perhaps?) I think it could actually be very useful when trying to do research online, especially with the note-taking feature.