As far as I can see, Address Book will not replace a proper PIM, although it might grow to be your one stop shop for contacts, both because you'll automatically use them for Mail.app and because iChat will also use it. AND it'll be integrated with cell phones that have Bluetooth/IRdA and vCard support (which many now have here in Europe). But for calendar functionality, a PIM is still needed. Integration for Mail.app would be good, integration of PDAs should be a high priority, although I've stopped using them. My cell phone is my PDA, and my TiBook is my PDA.