We have an iMac, MacBook Pro, a Windows laptop and a Windows desktop (all for business-use). So I have experience with both PC and Mac. For both the platforms there are pros and cons. Here are some that come to mind:

Windows based system pros:
-Relative cheap to purchase
-familiar lay-out to most people

Windows based system cons:
-System clutters up in time, making the system slow
-Windows uses a up lot of resources
-System needs constant maintenance to assure smooth operation
-Upgrade from one Windows version to the newest version is expensive

Mac system pros:
-a Mac WORKS, no need for constant maintenance
-installation of printers and other devices are super easy (yes, easier than Windows Plug and Pray)
-fantastic controls (mouse and touchpad) and intuitive lay-out
-cheap to upgrade from one OS to the next
-Windows can be run on a Mac
-great design

Mac system cons:
-Mac does not support Flash; certain web-content is not visible
-when connecting to a Windows Exchange server for webmail you are limited to use the light version
-Initial purchase is more expensive than a PC

Take into consideration the licenses for Windows-based software you may have. If you cannot migrate them to the Mac, you may have to buy new licenses. On the other hand: a Mac already comes with iLive, and iWorks is pretty inexpensive...

Mike
www.mikewever.nl