According to TechCrunch: it looks like a random sampling of people are getting to “vote” on the results that they receive for search results. This human element will help google know if their automatic algorithms are working well.
This will probably also be a new part of the Google Algorithm. It is currently in “bucket testing”, which is a random sampling of people testing the service without their knowledge. If Google gets a decent reaction and the service seems usable, they will release it to the experimental area where anyone can test this feature.
Google continues to dominate the web space. I look forward to seeing their next “big” idea.