Google+ just added that feature last Wed. I can 'share' a circle with you, but it only sends you a 'snapshot' list of current members of that circle, allowing you to add those folks to any of your circles. It won't reflect any future changes or allow you to see the posts to my circle. I'll stop with the G+ talk here and send you a link to a description of the feature on G+.
Originally Posted by Toffle