I'll throw my 2 cents in . . .
I have a MacBook (base model: 2.0GHz Intel Core 2 Duo, 1GB memory, 80GB hard drive, Leopard 10.5) Parrallels running Windows XP) and a G4 iMac (1GHz PowerPC G4, 1.25GB memory, 120GB hard drive/500GB external, Tiger 10.4) at home. Work on a Dell Precision 380 tower (3.6Ghz Pentium 4, 2GB memory, 80GB hard drive) at work.
I'm a landscape architect (and amateur photographer), so work with AutoCad, Sketchup, CS3, etc. Just installed CS3 on both macs at home, and also Lightroom, and haven't had any problems. Sketchup 6 also installed (btw, there is a patch on the webs that fixes the Leopard freeze problem, was a problem with the graphics driver. ran it, and SU works perfectly now).
As everyone has said before, if you are a casual/amateur user, then macbook/macbook pro works great for these programs. Not as fast as my Dell at work, but not sure you can really compare the 2. Never have owned a Windows laptop, so can't comment on that as well.
I will say that I have decided to buy a Mac Pro sometime in the future, as my iMac is now infuriatingly slower than my Macbook, and using the book as my primary graphics workhorse is not practical for me.
If you are a poweruser, and are familiar with Unix, than OSX is fantastic. It allows for endless scripting to improve workflow, without the need to buy any extra software. Most people are not, so this aspect of OSX is usually overlooked.
I will say that most people, including myself, are partly drawn to Macs for the design factor. I never really try to convince people to buy Macs, as it is indeed a personal preference.