Are you having issues with Apple AddressBook after upgrading to Snow Leopard? Are you seeing the Beach Ball of doom show up each time you launch AddressBook?
If so this may be the solution you require….
1. Navigate to ~/Library/Application Support/Address Book
2. Delete this file: AddressBook-V22.abcddb
3. Then open the MetaData subfolder
4. Search inside MetaData for the term “smart”
I then deleted any smart group that I knew contained a negative statement. The group I deleted was “No Group” as its looking for cards that have no group. Once you are done with this Apple Mail & AddressBook should work perfectly. My recommendation is NOT to add the smartgroup back in, until there is a fix.