Import Gmail contacts into Apple Mail.app
Update: The instructions below are outdated. The best way to export Google contacts is to go to Gmail, click Contacts on the left, and then Export. From there, it should be obvious how to export for Apple's Address Book. But even better than that is contact syncing, which you can set up in Contacts.
Just keep in mind that Mail.app, and most Apple/Mac apps, use Address Book to store contacts.
Want to import your contacts from Gmail into Apple's Mail app?
Despite the fact Mail has no “Import contacts” feature, it’s actually easy. [Edit:] Note, however, that when I followed these directions, the full name of Gmail contacts became the first name of Mail.app / Address Book contacts, not a huge problem, but it meant searching by last name was broken.