Escaping from Google Contacts 

Contacts makes it very easy to export data.  Visit the main contacts page directly, or within Gmail.  At the right near the top are links called Import, Export, and Print.  Click the Export link to initiate the export process.  You can export in several formats, each appropriate for various other contact applications.

Escaping to Google Contacts 

Contacts also accepts imported data.  Again, visit the main contacts page directly, or within Gmail.  At the right near the top are links called Import, Export, and Print.  Click the Import link to initiate the import process.

Keeping in sync

Often, you don't want to escape completely in either direction, but rather maintain up-to-date versions of your contacts in more than one system.  The Google Sync Services page tells you how to do this.