Cad
It depends on what knid of CAD you need. The heavy Hitters, ACAD and microstation are both currently PC only (although there is recent talk about ACAD porting to the MAC and MStn will no doubt follow. For big projects they are both the most stable and the most conducive to multi user/discipline environments. That said, under either Boot camp or one of the Virtualisation Applications (VM Fusion or Parallels) the PC versions work perfectly well, with no perceptible performance hit. Given how expensive CAD licenses are, I would recommend you port to MAC, get a copy of Parallels 4, and use your existing package - pretty much natively. Ive been using MCStn V8si for a few years now on a Macbook Pro and find it work fine. I drag and drop files to the mac desktop and can print either from Windows or Mac.
CAD remains the last bastion application to go back properly to MAC. The barrier remains the fact that the majority of heavy license users - Engineering and Local Authority/Public Gov users are Microsft and PC based from years gone by. If anything, its design professionals - architects etc, who are pushing for availability on both platforms.
Hope that helps. Good luck.