Understanding the +1 Buttons in Google+
There are two types of +1 buttons on the Google+ social networking site: +1s for websites and +1s for individual posts inside Google+. On posts inside Google+, it’s like giving a person a high five, letting them know you liked their posts. In some ways, the +1 button is similar to the Facebook "Like" button.
The +1 buttons help search results appear more relevant on the web and Google search results (by showing you results your friends have shown interest in) and they also appear in your Google+ profile. Beyond that, the +1 doesn’t do a whole lot yet, but Google+ could expand the feature in the future.
There are two major differences between the +1 button and the Facebook Like button at this point, including:
On Facebook, a "Like" subscribes you to a post’s content and you get notifications for every new comment on that post. On Google+, you don’t get notifications for the posts you +1.
On Facebook Like buttons for websites, while liking the website adds it to your interests in a similar manner to how Google+ adds it to your +1s tab in your profile, Facebook also allows website owners to publish content to the Facebook streams of those that have liked their website. On Google+, at least at the moment, website owners can’t publish to the streams of those that have +1d their website.
Even though, compared to Facebook, the Google +1 button doesn’t do much right now, you should still consider using it anyway — it’s a great way to just show someone you’re listening and that you like their post without doing much. And, as mentioned earlier, Google+ is also likely to expand on the functionality of the +1 button over time.
Just like Facebook does not have a Dislike button, Google will likely not have a −1 button because −1 is, well, negative. Both Google and Facebook seem to agree that it’s much better to give users a positive experience than it is to encourage a negative, and a −1 button could definitely bring negative feelings to the service.