I'd never buy one new, but i've bought a number of them used (and even used they are about as expensive as a new dell). Still, the quality is second to none, both in terms of longevity and components (the graphics card on my Pro is fawking awesome). Then add-in the fact that you can dual-boot with Windows 7 64bit and you have the best of both worlds.
But honestly the main reason I switched to Mac's is the security issues, read up on how many ways there are to gain full control over a windows system, it's essentially like having everything on your computer/network open to whatever hacker would like to take a peek. Fuck-that.