Nope. My computer is Microsoft free right now. I chose Mail/Address Book/iCal for a few reasons...
1. As a switcher, I wanted to really give the whole Apple lifestyle a chance. I started out trying the Apple apps, thinking I might not like them because my brain was so Outlook dependent. Honestly, I didn't think the Apple apps would be robust enough for me. After viewing the preferences and comparing them to those in Outlook, I assumed they were severely lacking in features. Turns out, the Apple apps did do everything I needed them to do. Outlook must have a buttload of features I just never used.
2. I have 2 Macs, and use my .Mac account to sync all my stuff. I also like having them synced to the Web, so I can access them from somebody else's computer in a pinch.
3. iPhone integration. I'm just assuming it's better since it's Apple-to-Apple. Never gave Entourage a chance, though.
4. The separation of apps doesn't bother me. In Outlook/Entourage you click in the sidebar to go from one function to the other. In the Apple apps, you click in the dock. So, the next function is still a click away, regardless of whether they're in one app or three.
5. In Outlook I had experienced too many problems with large .pst files.
Obviously Outlook and Entourage aren't the same app, but I did assume (perhaps incorrectly) that issues I had with Outlook had the potential to be problems in Entourage too.