I have Fusion on my MacBook Pro and used CS2/Win on it a while ago. Nasty nasty. (okay not nasty but much slower) I don't recommend using any big program in a Virtual Machine..
Well, he was talking about BootCamp - meaning running CS3 natively - and not about virtualization.
Why Apple had to assign a stupid marketing name to a multi-boot feature and a driver collection for Windows is beyond me, but at least they managed to confuse everybody with it.
So when you use "BootCamp", that just means that you use your PC to run Windows instead of OS X. Yeah, that's right: Your PC. Because technically, there is no difference at all between a Mac and a PC - it uses nVidia, AMD/ATI and Intel chipsets like any other Dell or Toshiba or Acer or Asus or Lenovo machine out there. It only has an Apple design, that's it.
So CS3 in "BootCamp" will run as good as it does on any other Windows machine with the same technical specifications as your Mac. However, there's a chance that CS3 in BootCamp will perform better on the same machine as its Mac version.