Meaning, if you want to give your partner, developer or a friend or family member access to login to your Google AdSense account to see reports or manage ads, you no longer have to give them your Google Account username and password.
We currently support two types of users on an account: Administrator and Standard user. Both types of users have full access to the AdSense interface, but only Administrators can add or remove users. As a publisher with an approved account, your access level for your account has now been set to ‘Administrator’. You can invite other people to access your account, designate them as Administrators or Standard users, and later change these settings if needed.
To enable this sign in to your account, visit the Home tab, then Account settings in the left hand panel. Then under "Access & authorization," in the "Users with sign-in access" section, enter the email address of the user you want to share your account with and click Invite. The user is added to the “Users with sign-in access” table with the status “pending.” Once the user has accepted your email invitation by clicking the link in the email and associating their Google Account with the AdSense account listed in the invitation, their “pending” status will disappear from the “Users with sign-in access” table.
When I tried this, I received an error that read, "currently being used by an existing AdSense account." Others are also receiving this error but they are not sure why.
Forum discussion at WebmasterWorld.