I suppose you have read this? It's from apple support (
http://docs.info.apple.com/article.html?artnum=107469)
.Mac Address Book: Custom Labels Do Not Sync
After syncing the Mac OS X Address Book on your computer with your .Mac (pronounced "dot Mac") Address Book, any custom labels you gave contact information (such as "Mom's" instead of 'home") do not appear in the .Mac Address Book.
Symptom
Custom labels do not sync to your .Mac Address Book.
Products affected
iSync
Address Book
.Mac Address Book
Solution
The .Mac Address Book syncs the "home" and "work" labels for most fields, and "Mobile" and "Fax" for the phone fields. The .Mac Address Book does not sync fields with custom labels.
Many scripts used to import contact information from other applications assign custom labels to fields that are labeled with "home" and "work". These are not synchronized either.
Note: This data is not lost, it simply cannot be viewed from within the .Mac Address Book.
To resolve the issue:
1. Open the Address Book on your computer.
2. Change the custom field labels to labels the .Mac Address Book can use.
3. Sync again.
So, no actual solution there. Hopefully in a future version?