Google+ likely won't challenge Facebook for social networking supremacy, but for many people, it will be an immensely useful product. It adds a number of innovative, not-yet-seen features to social networking, such as Sparks. More important is that it puts you in control of what you share with people; lack of that control is one of Facebook's greatest drawbacks.

Incidentally, even if you're not signed up for Google+, you may have noticed some changes in other Google apps, such as a new "People Widget" on the right side of the Gmail screen that offers information about your correspondents (similar to the add-on), and a new black navigation bar on some of the other services, such as Google Calendar. Google is obviously gearing up for a big push.

Because the service is in such a limited release at this point, it's hard to know how useful it will be. If people sign up in droves, it will clearly become a must-have site. (You can get information about availability .) If they don't, it will likely wither away.