I am living a lie: I have owned a dual core macbook pro for over a year now, and I am writing this comment under windows. Shame on me- I love boot camp.
Microsoft Outlook is iCal and Address book in one. It has a calendar, an address book, groups, email and pop-up reminders, syncs with phones, pda's, and black berry with bluetooth.
Same set of discipline and outlook is a PC users best client database. The newest version of Outlook has business contact manager that also does a great job of further refining your clients.
It has marketing, sales, and project tracking that integrates with contacts and e-mail.
My trick to manage using Mac and PC on one computer- I let my blackberry do all the work.
Just sync the blackberry to the Mac side, restart in windows and sync again and I am golden. No matter what OS I use I get alarms to be productive.