"Many of the best photos, articles and videos we find online are the ones recommended by friends. So we're making it easier to discover these recommendations in your Google+ stream. Starting today, we'll occasionally highlight posts that were +1'd by people in your circles and if you +1 a post, we may highlight it to your friends as well," says Shimrit Ben-Yair, from Google.
Now +1s for Google+ posts have more value because they're a signal for recommendations. If more people from your circles +1 the same post, then it's likely that you'll want to read it. +1 is now an indirect sharing tool: you're not sharing a post with anyone who is following you (or some of your circles), you're helping Google provide better recommendations. +1s are already used to improve Google's search results, ads and now the Google+ stream.
If you want to control who sees your +1 activity updates, go to this page and change the "visible to" value. The default option is "extended circles", but you can pick "public", "your circles", "only you" or a custom list of circles and people. You can check the posts you +1d here: it's an activity log that starts to show data once this feature is available to you. Google is "rolling out this feature over the next few days".
It's interesting to notice that the default visibility value is extended circles, which include your circles and the people in your circles' circles. That means your +1 can influence a lot of people.
Hopefully, Google+ will do a better job at recommending content than YouTube. Instead of only showing the latest videos uploaded by your subscriptions, YouTube also shows the videos they liked, their comments and more.