Hmm... My own theory - from actually working in a film visual-effects company - is that whatever operating system you're *forced* to use at work, you inevitably start developing an intimate hatred for...
I use Red Hat Linux for 8 hours of every working day, and despite the fact that it's blatantly the best OS for the job, I've learnt to despise it. Its like a breath of fresh air going home and wandering through the bright happy summer meadow that is Windows XP (with Firefox installed of course - I'm not *stupid*

)
If commercial politics alone have forced Pixar to use a purely Mac based network for CG production - they probably hate them with a passion - Macs are fine for editing, okay for compositing... but utterly underpowered and comparitively useless for 3D work...
- anyways, I reckon Steve is absolutely over the moon about SNM being on PC