GET BACK TO WORK MOTHERFUCKER!
That being said. I like to consider myself relatively unbiased in the computer market. I have my preferences, and I can back up why I prefer X Y or Z, but when it comes down to it, 9 times out of 10, I'm just as effective on any machine.
I, personally, prefer apple-built hardware because it just lasts forever in my experience. I mean, right next to me, I have an iMac G4 that I use as a media center that was HORRIBLY abused by both my family, and the secret service, and it still runs beautifully (save for the dead backlight on the screen). Well worth the extra money.
As far as an OS, I choose OS X over Windows due to the UNIX base, and OS X over Linux, because of the way that programs are managed (an OS X .app is just a folder with an extension, it's really just a container), I find it much easier than Linux's "Executables everywhere" approach, and Windows's Registry system
Well, there's that, and as far as the OS X/Linux things go. I also just like some OS X apps better (for example, OS X's Adium is better than Linux's/Windows's Pidgin, which it is built off of)