This is kind of similar to the existing weather plugin:

The task is to create a "Social Plugin" that displays the avatars of people on the globe and some more information in a tooltip. Clicking on the Icon should start a webbrowser that displays the opendesktop page with the entry related to the avatar icon.

See:

http://freedesktop.org/wiki/Specifications/open-collaboration-services

The login/password information for the social plugin should be specified inside the render plugin's configuration dialog.

See

http://techbase.kde.org/Projects/Marble/OnlineServices

for creation of Online Services.