I'm a long time hardware hacker and programmer, and have used (and programmed for) many systems: TRS-80 (color and B&W models), Apple II, Atari-400/800, numerous custom hardware platforms, original IBM PC (MS-DOS, most versions), PC clones from 8088 through latest Pentiums, Sun Sparc 5/10, Sun UltraSparc II, Coherent, OS9, OS/2, Linux (Slackware, Redhat, Mandrake, Debian), Windows 3.0/3.1/95/95/NT/XP -- I know I'm missing some here; these are the ones I can think of off the top of my head. I am a real computer junky with at least a dozen computers strewn about the home.
I have always loathed Apple's Mac computers. I always found them to be "dumbed down" machines with no compelling technological advantages.
After extensively looking into OS X (and buying an 800MHz, 1GB, 17" iMac w/superdrive) I have been won over. I was running Debian GNU/Linux as my primary desktop, but now the iMac has assumed that role.
Beyond just oogling the pretty applications on the iMac, I have really used it. I learned both the Carbon and Cocoa programming models and learned Objective-C. I researched the G4's CISC architecture and assembly language instruction set. I use the iMac every day for my work, which covers an extensive range of programming/development tasks. While Mac OS X has it's flaws, and the Mac hardware is a little pricy, it is by far the best desktop environment I have ever used or seen. While I still prefer Debian Linux for a server environment, Mac OS X provides a superb desktop environment.
To those who use GNU/Linux for its free aspects -- you are a bit misguided. I'm completely behind free software, but [IMHO] the Linux kernel is a dead-end road. Please support the HURD kernel, instead. The HURD is a far superior architecture and is also an idealogically better choice with regards to free software.
My two cents.