Orkut has been in the midst of privacy and security concerns since its launch. There have been many ways through which you can get to know the email address of any person on Orkut even when it is not displayed in the public profile. Although, Google keeps on fixing bugs as and when they are highlighted; however, there seems to be a long way before they can make Orkut a secure social network.
One of the method to know the email address which I came across has been listed below which you can try yourself.
1. Open the profile of the person whose email address you wish to know. It can be anyone in the Orkut network.
2. Click on "Ignore User" link as displayed in the screenshot below.
3. Open GTalk and sign in with your ID
4. Click on Settings and select "Blocked"
5. You will find the email address of the person whom you blocked on Orkut.
Let's see how much time Google takes to fix this bug. I am sure before that a lot many email addresses would have become public.