Google Reader Shared Items Page
By default, Google will pull content from your Google Reader Shared Items page to Buzz. That makes sense since you wouldn't be sharing blog posts you found interesting unless you wanted others to read them. But if someone clicks through to your public Google profile from Buzz, and you've got Google Reader listed there as one of your links, then once again you may have exposed your Gmail username.
Just like the URL for your Google profile, the Google Reader Web address may display your Gmail username by default, like this: "www.google.com/reader/shared/johndoe."
So if John Doe wants to keep his username private, then just as with his Google profile Web address, John needs to do change the default URL for his Google Reader Shared items page. The result would be something like this: "www.google.com/reader/shared/09876543211234567890."
To change your Reader URL, visit Google Reader and click "sharing settings" on the right hand side under the "People you follow" section.
Picasa
Now that your Google profile is more public than ever, you may want to figure out whether or not you want to include links to Picasa from your profile and which photos you want to make public.
Again, your Gmail username could be part of the URL for your public photo gallery, like this: "picasaweb.google.com/johndoe." Fortunately, however, Picasa has better privacy options than many Google services.
Let's say that 'johndoe' actually wants to make his Gmail username public, but at the same time he doesn't want to make it easy for someone to find his Picasa photos. If that's the case, John has two choices: customize the URL for his public photo gallery or adjust the individual privacy settings for all his Picasa photo albums.
If John wants to customize his URL he can change it to almost anything he wants. So John can have a Web address for his Picasa account that is not his Google username, easy to remember and share with friends, but also a little harder for outsiders to figure out.
Visit the Picasa support pages to find out how to change your Picasa URL.
The other option is to change the sharing settings on each of your Picasa photo albums. Picasa has three security levels for individual albums, but the names of each level aren't as clear as they could be. So here's a quick breakdown:
Public: Anyone can see your Picasa album, and your photos could appear in public searches in things like Google Image search, Google Maps, Picasa Albums search, and the Picasa Web Albums Data API. You can learn more about public search on Picasa's support pages.
Unlisted: These albums use an authorization key (a combination of letters and numbers) in the public URL. Only people who have the exact combination of letters and numbers in the Web address will be able to see your photos. Google doesn't say whether or not these photos are included in public search.
Sign-in required to view: This is the highest level of privacy in Picasa, and only people you explicitly authorize will be able to view your photos. However, for this security level, anyone you invite to view your albums needs to have a Google account or will be prompted to create one. Again, Google does not specify on the Picasa support pages whether or not these photos are included in public searches.
Learn more about Album visibility options in Picasa.
Sign-out and visit your profile
The last thing you should do is sign out of your Google account and visit your public profile so that you see exactly what other people see. Look at the information collected there, visit the links (you'll want to sign out of those accounts as well) you've added to your profile and ask yourself, "Am I comfortable with this information being public?"
It's not about FUD
Before I open the floor to comments, let me just say that this is not about spreading fear, uncertainty and doubt (FUD). In many ways, I like what Google Buzz has to offer, and am an avid user of Google services. But I also recognize that your e-mail address is one of the most private aspects of your digital identity, and Google should not be exposing this information for some of its users so readily.
Your e-mail address houses your personal contacts, it's used as part of your sign-in ID on countless Web services, and it also happens to be one of the most direct ways that people can contact you. So you owe it to yourself to stop for a moment and examine how much of your personal information will be out there when you're using Buzz, and whether you're comfortable with that.
Connect with Ian on Twitter (@ianpaul)