Well, I use a Macbook Pro and I've used a PC for a long time. I can tell you that Macs are great, but the greatest thing is that the Macs out right now support both Mac OS X and Windows XP/Vista. You can boot either OS and it works great.
Most of the 3D apps are available for Mac, 3DS Max and ZBrush 3 are not available (ZBrush will come soon, I think).
There are no real advantages for Mac over PC, the apps are the same. The OS is more stable than XP/Vista, but that all depends on how you use your computer. If you're a responsible user Windows is just as stable as Tiger. Then there's the visual part. In my opinion Macs look and feel much better than PC laptops. But that quality is something you pay for, Macs are generally more expensive than PC's. But, Mac laptops generally stay useful for a long time, I've used my previous Powerbook for 6 years, never a problem.
The Mac OS, Tiger, is great. Very stable and slick. Unlike Windows you don't have to worry about viruses, which is great. In October the new Apple OS will debut, Leopard, and it's looking very impressive.
So yeah, me being a Mac user I would recommend a Mac. You don't lose the functionality of Windows because you can use XP/Vista on your Mac. It is even possible to have Windows apps inside Tiger, using Parallels. Also, they look great and just work. On the other hand, they're more expensive, and especially with laptops you have no real upgrade possibility. Maybe a hard drive, but no graphics cards. But if you want upgradability you should buy a tower PC/Mac, and no laptop.