I'm not trying to take a shot at Mac users when I say this - in fact, I'm a Mac user myself at the office, as are most of my colleagues (I use a PC to develop and run most of our web apps though). I think it's fair to say I'm taking a shot at Apple.
My new PC is three times more powerful than JZ's Titanium. It's over �1000 cheaper as well. I can run a choice of operating systems (Windows, Linux, Unix) and can choose from a huge range of software of all kinds...can you get many games for the Mac? I've never seen many...I'm sure there's more that could be said.
In my very humble opinion, Jeffrey's Titanium just don't cut it when you compare it to that. The cost alone is prohibitive - laptop PC's are far more powerful for that price.
The Mac machines I use in the office are desktops, laptops from older to new machines. I'd trade them in for a PC any day of the week - and from talking to my colleagues, most of them would as well, and they don't even use PC's...just their work machines.
Just my 2cent.
AppleMatters Interview: Jeffrey Zeldman Talks Apple