I guess it's just a matter of preference. I love the fact that my BlackBerry syncs seamlessly and completely with my outlook contacts, but that just fits how I use my contact database. I wonder if there is a way to create a second contacts database or group in outlook that wouldn't sync to you BlackBerry.
The other side of the argument is that RIM decided to use a fairly widespread, and powerful existing PIM application instead of forcing you into a proprietary application. (even though Outlook IS proprietary to Microsoft, it is one of the most used PIM applications on the planet, expecially in businesses)
Again, I guess it just boils down to how you use you PIM info.