Google is trying very hard to get people to integrate with its Google+ services, although the latest update may be going a step too far. Beginning soon, anyone will be able to send email to their G+ contacts without knowing the recipients’ email address. This may not seem like much, since nobody actually goes on Google+. However, anyone with a Gmail account is automatically signed with an account. Which means that almost everyone is involved.
The service will roll out over the next few days, and email coming through the service will be sent to the new social tab that Google introduced not too long ago. Your email address will still be kept from the person sending you the message; unless you decide to respond to it. Essentially, it is turning Gmail into a private messaging service for G+.
Users can still opt out of the service by turning it off; although it is also possible to just limit the number of people who are able to email you via G+. The Google Blog says that the feature is slowly rolling out and users will receive an email with a link to the option to turn it off.
[source: Wall Street Journal]