No, if you use Picasa, people who have access to your history can find your gmail address.
http://theharmonyguy.com/2010/02/12/using-google-buzz-can-ex...
In my testing thus far, it matters little whether you’ve
Picasa before – if you have a Gmail account, Picasa is also
enabled on your account. And while individual Picasa albums
have privacy controls, I have not found a way to block simply
loading your Picasa home page.