It is a bit embarrassing that I've probably spent seventy-five percent of the uptime running Windows XP through Boot Camp. (Look, Team Fortress 2, okay? Lay off.) But it's a nice, beefy machine, and it runs both operating systems well. I'm genuinely impressed at how faithful the Windows XP experience is -- I've had the machine for all of a month or two and already Windows Explorer crashes on a regular basis.
If I had any real complaint design-wise, it would be with the Mighty Mouse. If Apple does have a fatal flaw it's that they can get too wedded to the apparent coolness of their designs and stick to it at the expense of functionality or even basic common sense. The Mighty Mouse is a perfect example. Instead of just, you know, having two buttons, it has a single button covering the whole top of the mouse and some sort of sensor behind the button which tries to guess if you pressed the left or right side. The best you can say about the sensor is that it's frequently accurate, though you can get accustomed to its quirks (don't get me started on the almost-impossible-to-push "squeeze" button, though.) However, one very obvious problem remains: since the sensor only detects one "button" you can't press the left mouse button and the right mouse button at the same time! I remapped secondary attack to the shift key in TF2 -- this works surprisingly well, by the way -- but generally speaking it's a headache for Windows use. Sorry, Apple, you struck out on this one.
Quibbles (and a few XP setup glitches such as the weird default microphone settings) aside, I'm happy with my purchase, and here's a list of useful software you should get if you decide to make the switch.
Cyberduck - Excellent and free open-source graphical FTP program. Get this, use this. Do not download ClassicFTP from Apple's website; it's remarkably slow and awful.
BootChamp - Boot Camp has a minor flaw in that there isn't an easy way to switch from Mac to PC and back after turning the machine on. You have to go to Boot Camp preferences and select the other OS, then reboot; but that permanently changes your startup setting, which is generally not what you want. BootChamp is a tiny little script that you can just throw on the Dock, which reboots the machine into Windows without the need for any messing around with preferences screens.
xscreensaver - This famous collection of screensavers works on Mac OS X.
HFSExplorer - The HFS (Mac) and NTFS (PC) file systems on the two partitions of a Boot Camp system don't get along very well. The Mac can read from but not write to the PC side, and the PC side can't comprehend the Mac side at all. Surprisingly there are no good solutions on the Mac side that don't involve paying someone money, doing scary surgery to the operating system, or both. But HFSExplorer is a great free tool that runs under Windows and can read Macintosh file systems; it's set up right out of the box to let you view your Mac partition and extracting any files you want is no trouble at all.
Some Community Codec Pack or Other - If you go to some big box store and buy a PC, it always comes with a bunch of really terrible software pre-installed, including a terrible DVD player, which most people uninstall or just try to ignore. But that does mean it'll have a DVD codec preinstalled as well. Thus, if you're used to the big-box PCs you'll be surprised to discover your XP installation can't play DVDs. Just, you know, go get the codec from the Web somewhere. You can find it. What, am I your mother now? Sheesh.
Jets 'n' Guns Gold - Well, you're going to need something fun to relax with after all this messing around, aren't you?