Thunderbird, Mac OS X, and vCards

IMAP problems forced me to temporarily switch from Apple's Mail.app to Mozilla Thunderbird (at work, I use it all the time under Linux). Trying to get my Mac OS X address book contacts into it, I did some research:
  • Thunderbird 3.1 Beta supports the Mac OS X address book.
  • The extension MoreFunctionsForAddressBook can import vCards into the Thunderbird address book (and you can select multiple Address Book entries and export them as a .vcard file).
Alas, Mail.app still does not support tagging. It would be nice to have an interoperable standard here (GMail's labels are implemented differently from Thunderbird's tags).