That would be an innocuous use. A worse case scenario is the guy who kiddingly writes a Google+ post about a vat of sex lube and then winds up endorsing it in ads -- as has happened on Facebook with Sponsored Stories. Like
You go to this page, and you make sure this box is unchecked:
According to the New York Times, Google's not actually ready to put this into use yet, but it "wants the ability to create such an ad unit in the future and is notifying users in advance."
Contrast the opt out process with Google competitor Facebook, and it will seem pretty impressive. While Facebook lets you opt out of "social ads" which are similar to what Google is doing, it does not have a one-stop setting for opting out of Sponsored Stories. Atlantic Wire has a good explainer on the difference between them here. Even after being sued over Sponsored Stories and paying out $20 million in a class-action settlement, Facebook privacy director Erin Egan told me, "Nothing has changed in terms of how the Sponsored Stories product works. We added language [to our data use policy] that was required by the settlement – adding an example of what we mean. It's expanding the language, not changing the terms. Controls are the same today as they were before."
Those controls consist of selecting the privacy settings for each individual thing you do on the site -- comments, likes, etc. -- that could potentially be sold for a Sponsored ad. If anyone but you can see it, it could be repackaged as an ad and sold to those people who can see it as a Sponsored Story.