An unexpected side effect of enabling Google Buzz is that your Google Profile automatically becomes searchable. Until now, you could edit your profile and only show your nickname publicly. When you activate Google Buzz, it automatically enables this option: "Display my full name so I can be found in search" and your full name becomes searchable. Google mentions that "changing your name here will change it in all Google products".
If you try disable the option in your Google profile, you'll no longer be able to post a new Google Buzz message until the option is enabled. Google will show this message:
That means Google Profile Search indexes all the profiles of Google Buzz users. Since Google Buzz is automatically enabled if you use Gmail, almost all Gmail users are listed.