Today Google engineer Owen Prater announced in the video statement above it is now possible to share Circles on Google+. From your Circles page, you can now select to share one Circle with any other. A post will be made allowing others to easily view and join the circle you’ve shared.
Shared circles wont continue to update as you make changes, however, allowing you to keep future changes to a Circle you’ve shared private. Others won’t see what you’ve named the circle either. Try it out!
From the announcement:
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Starting today you can actually share your favorite circles with others! So if you’ve got a great Photographers or Celebrities circle, for instance, then you can share a copy with your friends.
To get started, just click on a circle from your Circles page, and click Share.
(Importantly: when you share a circle, you’re only sharing its members at that time. Also: the circle name is always private to you, and any changes you make afterwards are private as well.)