First off, let me say this to all of the Mac fanatics out there;
NOT ALL PCs RUN WINDOWS!!!
Sorry, but I had to yell that since most of the arguments that the followers of Saint Jobs use to bash PCs are the same arguments the Penguin-powered crowd use against Microsoft. By that logic, beef if evil because McDonalds burgers tasted like crap.
Now, I could just direct you to this comaprison of Windows and Linux but I think I will just leave that link and add my real thoughts.
Linux and OS X are both UNIXoid systems. OS X is loosely based on BSD UNIX whereas Linux is basically a freeware version of UNIX for the x86 platform. Since they are basically the same under the hood, they both have the same (high) resistance to malware. Read The short life and hard times of a Linux virus and realize that it’s easily possible to have a safe PC.
On the CAD front, I like BRL-CAD but it is cross-platform (including Mac) so I don’t think you’ll have any problems. Of course, since CAD requires a lot of number crunching, a Core i7 may be better at it than most Macs and would definitely be cheaper.
Oh, wait… you can’t get a Macbook with a CPU based on the Nehalem architecture… but you can get a PC laptop with the Core i5.
Battery life… Linux tends to be a little more efficient than Windows due to better power management, but I must admit that Macs have an edge there. Sometimes. I’ve seen 10+ hour PC laptops, and an extended pack can easilly get you 5–6 on most models, even the most power-hungry ones. I’ve also seen many Macs only get half (or less) of what the flashy ads say they should because of the difference between reality and “best case scenario”. (Translation:advertising lies.)
However, once that battery runs dead, you are toast. The Macbooks I’ve seen don’t let you swap in a fully-charged spare pack. Also, in a couple of years when teh battery does what all LiON packs do, you are looking at a hefty service charge in addition to the price of the battery.
Gaming… very hit-or-miss. Some Windows games run fine under WINE or Cedega (a gaming-optimized version of WINE) and there are ways to get most Windows software to work. You might look here and here to see how Linux handles WoW.
Macs claim ease of use, but they lack it. Linux can easily be done up like so
They claim lower cost of ownership, but those comparisons are only to Windows systems. Most agencies (including government ones like the DOD) find that Linux is far cheaper. Look at a list of Linux adopters. Notables include IBM, Amazon, Google, and the aforementioned Department of Defense. Add lower cost of ownership to the inherently lower cost of PC hardware which runs about half of what a Mac with similar specs runs and I think you’ll see which way that is heading.
Personally, I’ve had many crashes with Macs and Windows but never more than a slight hiccup from Linux; none that required me to do more than restart the application. I’d say stability goes to the Penguin here.
Overall, I would have to say PC but skip the Windows.