I know Address Book metadata is stored in Library/Application Support/AddressBook.
I wonder, however, what's up with Address Book "Groups".
They are peculiar items. For example, I quit LaunchBar (it prevents deletion if it's running), then I removed all items from AddressBook, emptied trash, then started Address Book and watched Library/Application Support/AddressBook/Metadata get repopulated with the .abcdg files that define Groups.
Clearly, Address Book was getting them from somewhere! I was not logged into iCloud. I have the sense Apple doesn't like Address Book 'groups', I wonder if this is very old code.
I'm trying to find a way to clean them all out because of an iCloud Debacle related to EOL termination leading to a cascading and comical failure chain (which established, in my mind, that iCloud is a regression from MobileMe, which is saying a lot – details here — http://tech.kateva.org/2012/06/icloud-transition-went-as-expected.html).
One aspect of the failure chain is recursive Group creation (hundreds of replicated groups).
Any advice appreciated!
Update: one guess. I think they may be coming in from somewhere in a local cache of iCloud data that's not being fully cleaned out even after logging out from iCloud.
Best Answer
I think I can answer my own question, based on further experiments.
Once you sync an Address Book with iCloud, the data is, in a sense "gone" from the local drive. You can still see it all in the usual location, but it's a cached version of the iCloud data. (You can "move" contacts back to the local drive, but Groups are gone forever.)
On startup, even if you're not logged into iCloud, there's a process (a bug?) that recreates at least the Groups, probably from some local iCloud data store. (I do wonder if Apple has 'social' plans four our Groups.)
If you truly kill all iCloud accounts, including from both System Preferences AND from Address Book, and restart, it is possible to delete all from Address Book and not have files magically reappear.
There are many tedious details on this and other iCloud topics in a long personal multi-update blog post: http://tech.kateva.org/2012/06/icloud-transition-went-as-expected.html.
Suffice to say, these are coming from iCloud. If you never mess with iCloud (personally I'm going to wait for Mountain Lion!) you won't run into this bizarre behavior.