I just found out that if you review or +1 an app, it shows that to all of your friends, even if they aren't searching for that app in particular. I knew that if you were looking at a specific app it would show you any reviews by your friends, but I didn't know that it would actually show that app to your friends as a recommendation based on your review. So, uh, FYI, I guess.
And there seems to be no way to turn this off. Google says, "If you don't want a review you have written to be shared, you can delete it." It's a good thing I'm not embarrassed to be using a pill reminder app, but man, if anyone was using an app for anything more sensitive, that would suck to effectively not be able to leave a review without advertising it to all of your Circles.