I have been using my Macbook Pro 17"(Core 2 Duo 2.33 GHz, purchased December 2006) with 4 gigs of RAM for about a year and a half now. I chose to purchase an Apple when they had sufficient compatibility with SolidWorks through Boot Camp. At the time I was buying, it beat out all of the Windows notebooks in the same price range.
For non-SolidWorks work, I use OS X. I had been exposed to OS X and OS 9 during high-school architectural CAD training, but never worked on a Mac operating system for any extended time. All of my personal computers were Windows based. Learning to use OS X effectively took me a couple of weeks. I found myself digging too deep to find options that were actually right under my nose. I was used to right-clicking my way through a tree of menus to find the option I wanted. In OS X, the options were all where I would have looked first if I hadn't developed my habits in Windows. I find the tightly integrated package of day-to-day software (Mail, Safari, iCal, Address Book) easy to use. Microsoft Office 2004 or 2008 are pleasant to use. The only thing I can't do in OS X SolidWorks.
I am currently running SolidWorks Office Premium 2008 SP3.0 on Windows XP Pro SP3. I dual-boot using Boot Camp. The SolidWorks performance is exactly the same as on a similarly equipped Non-Apple notebook running Windows XP. Because the Macbook Pro doesn't use an integrated graphics processor, it is significantly faster than the Macbook for 3-D software. Mine has the ATI X1600 256MB graphics card in it, which runs relatively large assemblies well (several hundred parts). Medium-sized in-context assemblies using a top-down approach don't bog the system down, and PhotoWorks renders at megapixel resolutions are in the 5-10 minute range.
At this point, if you compare hardware accurately between Windows notebooks and Apple notebooks, pricing should not differ significantly. What I gained by going with the Apple is an operating system that suits my non-CAD needs better than Windows, and has been incredibly stable. I also gained more attractive hardware that I find more pleasing to work with day-to-day. Battery life is better than comparable notebooks, and the whole package is half as thick as competing units. I have not noticed any incompatibilities or detriments when compared to running XP on any other computer.
I hope this contribution is helpful.