One of the most popular new features in Outlook 2010 is proving to be the Social Connector. If you work in a corporate environment, this feature can hook into internal SharePoint 2010 services to deliver contextually relevant information as your browse your Inbox - such as who an e-mail sender reports to, their newly updated mobile phone number, and recent documents they have shared.
This feature is on by default, just look at the bottom of your message or preview pane for the See more about link to open up any available relevant information. At minimum, you'll see recent messages, attachments, and meetings - and possibly a lot more. Click the Add button to link this person to a social network, which expands the types of content you can pull in.
If you're not on a corporate network or want to further expand your social circles and pull in more feeds, you can get LinkedIn and MySpace add-ins (and, coming soon, Facebook and Windows Live).