It makes sense, but it’s a bit too complicated for the average user to accomplish. Along the same lines, it’s definitely too much of a hassle for anyone to go through to export data (they own?).

Paul Robinson of Vagueware writes:

On adding an application a user is invited to select all the friends the user wishes to export.

These friends are invited to add the application. They may choose who is allowed to export their contact data and personal information. Privacy controls would exist to allow groups to see certain data when exporting.

The original user may then ask for an export in XML format (maybe a collection of vCards) of all the friends in the system. This format could then be used by other applications, and libraries developed to allow integration with other websites.