The same functionality is available for Internet Explorer users in the new version of the Google Toolbar released today.

All new social networks are challenged by at least two questions asked by users: why should I use this and how will I be compelled to remember to come back? Google+ has probably not done a good enough job answering the first question yet. Too many people feel like they don't have a meaningful number of contacts to put into Circles and share with there. But the second question is solved in large part by the notification systems offered at the top of all the Google properties and now by these browser plug-ins.