On January 9th, Google announced that your Google+ contacts (people in your G+ circles) will now automatically show up as contacts inside of Gmail.
This isn't really a good thing, from my perspective. A lot of (OK, just about all of) my G+ connections are acquaintances or people who know me from the industry (many of whom I do not know personally). Making the ability to email in Gmail automatically visible to all of those folks feels like something akin a privacy violation. I don't really want to end up on somebody's huge CC list of forwarding some joke or political complaint. I think if folks want to contact me, they can go to my website and actually click on the contact me link.
I think this is auto contact enabling is a bad idea. If you agree and want to disable this new functionality, Consumerist explains how to do so: Go into "Settings" in your Gmail account, and under the "General" tab you will find an "Email via Google+" entry where you can change the setting so that "no one" of your Google+ contacts is automatically given the ability to send you email from inside of Gmail.