In case you're one of the many that are uncomfortable handing out your Google username and password to networks that would like to aid you in the friend invitation process by importing your Gmail contact list, Google now has a better solution for you. Google has finally released the Contacts Data API, which benefits both individual users and developers.
The Contacts API allows individuals to own their own contact data, use it in any manner they see fit, and import it and export it at will. Several of these benefits spill over to developers, who can now enable users to import and export data, and access their contacts lists without having to give you the personal information of username and password. The Contacts API lets the contacts list be shared across most of the major Google apps, including Reader and Calendar to name a few.