Earlier this year we added Google Contacts info to Google+ profiles. So when you're visiting a friend's profile, you (and only you) can see his phone number from your personal address book. (http://goo.gl/4hFZ5)
Starting today, you can also edit these details directly in Google+. Just visit a buddy's profile, click 'About', and add a birthday, an email address, or even a short note. Everything's saved in Google Contacts, so your address book in Gmail and Android will be updated automatically.
Let us know what you think in the comments!