Google says that 10 companies, including Fitbit and Shazam, have already implemented the sign-in feature, with more partnerships planned in the near future.
Google+ Sign-In also offers more features than just being able to simply log in using your Google+ account. The service makes it possible to decide what information to share with your Google+ circles, if any, so you’re not constantly spamming them with every status update and photo you post. The new service is available on the web, as well as on Android and iOS. Plus, Android users get the added ability to push any mobile app version of a service directly to their phone when logging in using Google+.
It will take time for Google+ to catch up with Facebook Connect and Twitter Sign-in, as app developers begin including the functionality, but if Google keeps at it and adds more useful features, it will become a major player in the social sharing sphere. Just today it was reported that Android beat iOS for U.S. market share in January, capturing 49.4 percent of smartphone sales in the last quarter. That's a lot of people with Google accounts.