If you have noticed the recent gmail chat changes, you would have noticed how closely google is integrating the google + with other google services. Now if you closely observe the pop up given below, it has been prominently integrated the google plus circles option.
So not only is the circle’s option right under the inbox options, its also there in you chat box. To be very honest, this is clearly aimed at getting more users hooked onto google + without letting them know. For some reason, we still don’t think it will help much as what the google + brand needs right now is a campaign designed to get groups to join and use it. Social networking works on groups, and if your friends are not hanging out on google plus, you have no reason to try as well. So that is probably the reason why so many people, in spite of joining google + are not using it proactively.
Rabbitricks 