Google quietly rolled out a new feature to its search today: Google +1. Essentially, it allows you to give a +1 to any link that comes up in your search results, and then your friends will be able to see what sites you thought were worthwhile.
You've gotta turn +1 on at the moment, via Google Experimental, but once you do you should notice the subtle change in your results. As you give the sites a little plus one, you should get slightly improved results. You'll also see when any of your friends have done the same, and those results will be higher up on the list.
It's clearly the early stages of something Google is hoping to make a key feature of search. Will it catch on? We'll see.