I am somewhat biased but even so..... :)
I know personally of four people who's computer came to the end of it's life recently.
They made an entirely different choice, an iMac or a MacBook, now they've apparently never been happier computer-wise.
If you
really need XP you can install a copy and dual boot, or cooler still, with VMWare or Parallels, you can even run both at the
same time :)
For the truly geek amongst us, Mac OS X 10.5 is actually a certified UNIX.
Vista drives me crackers, apart from it's sluggishness on existing hardware, it's the security (idiot!) that is the final straw...
"Are you sure you want to do that?" I clicked the flippin' button didn't I? Of course I flippin' well want to do that!!
.....and relax

-Rob
ps XP sp3 on my dual boot partitions btw.