Microsoft SharePoint Server 2010 supports two types of memberships: Distribution List (DL) memberships and Windows SharePoint Services site memberships.
DL membership information is obtained from the Active Directory directory service, and Windows SharePoint Services site membership information is obtained by pulling membership information from the SharePoint site. A user’s public My Site page, called the Profile page, displays the user’s memberships, as well as memberships the user and the viewing user have in common, among other information.
Membership is a first-class object in the User Profiles object model. You can get to the memberships from the UserProfile object.
SharePoint Site Membership
The user is member of the “Member” group for the site. All sites on the levels below will also show if the “Member” group exists in these sites.
The “Sites” memberships depends on Search. If you cannot see any sites memberships, try running a full crawl.
Distribution List Membership
The Distribution Lists memberships depends on the User Profile and User Profile Synchronization.
Note : You might also notice that Security Group Memberships are not shown. They are, however, displayed in the Newsfeed.