As promised during the 2003 MacWorld SF keynote, the at online address book in .Mac can now synchronize with your Address Book in OS X. In fact, if you’ve already been syncing your address book to .Mac with iSync, you don’t have to do anything but go into the address book preferences and turn on the synchronization. The online Address Book will then use the synced copy of your address book already sitting in your .Mac account and bring itself up to date.
How useful is this? Pretty useful, I think. There have been plenty of times that I, as a newly PDA-less person, wanted to have an address and was unhappy that it was only in my home address book. Now I just have to go to addressbook.mac.com and bang, it’s there. The main drawback to usefulness that I see is that the online version of the address book doesn’t preserve categories, so there’s no way for me to easily see just my family, for instance. But search works quickly and well, and the UI in general seems pretty clean and functional. There are even pretty instructions.
Here’s a screenshot (with names hidden to protect the innocent):