It took some time coming but a Google+ Share button has now been launched – http://googleplusplatform.blogspot.co.uk/2012/04/introducing-google-share-button.html
Google say it is more for when people just want to share something with their friends.
I’ve now added the new Google+ Share button to this blog and another site
A few hiccups already, it looks as though you can’t control the title, image, description when sharing anything and it is then displayed on your Google+ profile
Fortunately, you can then log in to Google+ and edit it out.
Surely better to have that option whilst sharing?