Practically, what this all means is that for the first time marketers can speak specifically to those users who they know something about and have already built a relationship with, either on Facebook or through a sign-up at a brick and mortar store, or an opt-in email program, or any other online or offline channel.

FORBES: Facebook's Ad Platform Finally Gets It Right

In an email, Biggar said that requiring an opt-in for her company's service would put real-world stores at a disadvantage as they compete with online retailers that track shoppers' behavior from the moment they enter a website.

WSJ: Schumer: Don't track shoppers without consent

Perhaps you acquired a list of subscribers that did not explicitly provide opt-in permission to receive your mail or you are still automatically subscribing email addresses obtained through trade show giveaways or other promotions.

FORBES: Email Ads: 4 Reasons Your Messages Are Missing The Inbox

That's not to say that your contacts need to opt-in to the search giant's social networking site to join the fun -- email invites are still available by typing your friend's address alongside your circles, or individual friends should you wish to plan an awkward inter-group soiree.

ENGADGET: Google wants you to join the party, announces Google+ Events (video)