If you have taken the latest Office 2010 Beta for a spin already, then you probably have noticed the Outlook Social Connector as well. Currently the only provider that can be used for this is a SharePoint server. Microsoft will later develop a Windows Live connector as well which allows you for instance to pull contact and related content information from Windows Live Messenger and SkyDrive. LinkedIn is also working on a provider for the Outlook Social Connector.
If you are a developer, you can create a provider for your own web service as well. You can find more information about it in this blog post of the Microsoft Outlook Team.