Macs are Macs. If you buy a Mac instead of a PC, you’ve got a Mac 
I’m typing this from a vintage 1998 “WallStreet” PowerBook. This computer has existed for almost a third of Apple Computer Inc’s total lifetime. I am not short on cash and could have upgraded to a newer computer if I felt it necessary (and it is, finally, getting to that point) but I don’t really have many complaints as a software developer.
Yesterday I did something phenomenally stupid and hosed a significant portion of the resources of OS X using a low-level 3rd-party hack that chose to die in mid-process. I could still boot but had no Finder. So I switched to booting from another volume using a simple Preferences Pane (equivalent to a doohickey in a PC’s Control Panel) and came up from a totally different volume, restored from backup, and despite some fingernail-chewing (because I’m nervous about deleting all files from my startup volume) it worked flawlessly.
We don’t have viruses or spyware. We are virus- and spyware-deficient over here in Mac-land.
I can run Windows 2000 or XP in emulation (Virtual PC) if I have to, but what’s far far easier is running NT 4.0 SP 6 in emulation. And you might be surprised at how much of current Windows software will actually run just fine under NT. WinNT Server just flies in emulation. And I’m on a vintage '98 PowerBook laptop upgraded to a G4/500, not exactly cutting-edge CPU here. A modern PowerBook can probably run XP at tolerable speeds. And if you get a PC virus you just throw away the virtual hard drive file and restore from backup.
It’s a laptop, not the most upgrade-tolerant of computer configurations, but in addition to upgrading the CPU via daughercard, I’ve added USB (via CardBus), FireWire (via CardBus), and can drive an external monitor as “extended Desktop” (yet again via CardBus but I’ve only got 2 slots so I only get 2 out of 3); upgraded the RAM to 512 MB; upgraded the HD several times, currently running a very fast 60 gig 7200 Hitachi; and I’m running the latest Apple operating system (“Panther”) on it. That should give you an idea of the practical longevity you get from a Mac. The Mac you buy today could easily still be your primary computer, to your satisfaction, 5 or more years later.
Ultimately, though, they are just computers, and if you prefer a PC and don’t hanker for the MacOS there are some solidly built, no-compromises, significantly impressive PCs out there. The brand that strikes me as closest to the PC equivalent of an Apple Mac is Alienware. I myself am totally a MacOS person but if I ever wanted a PC to really use and rely upon in some situation, those Alienware boxes and laptops don’t look like compromises. In the cheaper vein, Dells seem decently built but after you buy them anecdotal info indicates you might be pretty much on your own. And even with that, they cut corners compared to Alienware or Apple.
If you’ve got a taste for Unix, go with Mac. It’s all Unix under the hood. X11, command line standards, roll your own from source code, etc. Mac is BSD tree Unix with a proprietary GUI but an X11 to handle nonproprietary Unix GUI apps.