July 31, 2011 will be the last day your Google Profile can be set to private. Due to the impending release of Google+, Google announced it will change how it displays profiles in a message on its Public profiles page:
The purpose of Google Profiles is to enable you to manage your online identity. Today, nearly all Google Profiles are public. We believe that using Google Profiles to help people find and connect with you online is how the product is best used. Private profiles don't allow this, so we have decided to require all profiles to be public.
Keep in mind that your full name and gender are the only required information that will be displayed on your profile; you'll be able to edit or remove any other information that you don't want to share.
If you currently have a private profile but you do not wish to make your profile public, you can delete your profile. Or, you can simply do nothing. All private profiles will be deleted after July 31, 2011.
Giving users a heads up should alleviate some privacy concerns, but it remains to be seen if Google's approach will help it avoid the same issues surrounding privacy that Facebook has encountered. Geek.com has posted a Google+ cheat sheet that may be helpful to users.