After I upgraded to Snow Leopard, I found an issue with Apple Mail and Apple AddressBook. Basically, after the upgrade I noticed these two apps took awhile to open. As soon as I would open Apple Mail I would get the beach ball of doom for awhile. Once it cleared I was fine but it did take about 45 seconds to recover from it.
It also appears that Apple AddressBook shows the same symptoms. The dreaded beach ball of doom kicks in when I would open AddressBook as well.
Believe it or not there is a simple fix if this is happening to you as well.
The culprit… SmartGroups that contain a negative.
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.