One of the most important aspects of Social Computing is the data.  Knowing what has happened, when it happens and what change happened is critical to providing a good idea of what has happened.  Most of the social networking sites now have some type of change log information displayed to the user.  For example Facebook, LinkedIn, and MySpace all have versions in your user profile page.

Facebook has a News Feed that keeps you posted about the current News of people you know.

LinkedIn has Network Updates that inform you what business colleagues are doing.

MySpace has Friend Updates to keep you in the know with your friends.

SharePoint has the same thing as Lawrence points out in his blog post on Social Networking called the Colleague Tracker Web Part.
http://blogs.msdn.com/sharepoint/archive/2007/10/24/enabling-and-managing-social-networks-for-business-use-with-microsoft-office-sharepoint-server-2007.aspx

One of the biggest things that most people don't realize is that SharePoint provides the ability to get this information back from the database using the object model. 

Create a query to pull back the information you want using the SPChangeQuery Class then use the SPChange Class to pull back the specific information and display it however you want.  These objects really just display actions a user has performed and will require some effort to display it like the colleague tracker web part.  Lucky for you SharePoint also comes with a Change Log object for user profiles that is part of Microsoft Office SharePoint Server 2007 (MOSS).  This object is the UserProfileChangeQuery Class.  You still use the SPChange Class for each instance but the information you can query is user profile centric.

Try coding it for yourself with the example on Microsoft's site: How to: Get Recent User Profile Changes Using the Change Log