you probably don't hear this much but it's not for what i can do on the Mac as it is what I couldn't do on XP. I leave my machine running all the time (usually).
17:28 up 8 days, 11:43, 8 users, load averages: 0.99 0.67 0.56
Stuff like 'cron' matters to me. Having a shell matters to me. Not fucking cygwin, a real shell. And a single vendor that makes the whole package work well (Apple). I didn't get that with Linux and I don't get it with Windows, but Apple has it. That's not important to most people, but for me it's huge. Now, there's all kinds of stuff I do on the Mac now which I can't imagine how I'd do it on a Windows machine.
For me to try switching from a Mac to Windows is almost harder than switching to a Mac from Windows now. There are Mac-only packages I use that have no direct equivalent on the PC. I'm glad there is some decent alternatives to QuickSilver on XP/Vista now but I think they all want money. That would be for example, the first thing.
Another example ... I can't imagine going back to Visio after having used OmniGraffle. I mean, no contest.
I get way more shit done on this computer than I ever have. Even with the inconsistent keyboard layouts.