Active Directory Federation Services (ADFS, formerly known as "TrustBridge"), is a future identity and access management solution which provides a secure environment for managing user identities, authentication methods, and access rights across an organization's various departments, offices, and regions.

This will make the SharePoint Extranet scenario very much easier to manage. For example, with ADFS - an administrator doesnt have to manage individual accounts of their partners employees. No longer do they need to worry about employees joining/leaving a partner or having the hassle of resetting a forgotten password.

The .NET Show on ADFS