Photoshop CS runs just fine on Mac OS X. You'll probably need to add a memory card to your bill if you're processing large images. My iBook with 640MB RAM had real trouble processing a 7x15 meter graphic, but that's quite an exceptional case. You're running on Unix so you've got all the batch editing comfort of
Image Magick from the command line without much fuss.
Pro's:
OS X - an O/S that just works. No really.
Tapping into 25 years of interface design expertise.
Apple - a company that understands technology is not just business.
Solid hardware design.
Cons:
It's not linux so you miss out on a load of software. Luckily with Fink, you've got almost everything ported.
Mac OS X is the best of both worlds - a great interface sitting on a powerful UNIX core - and the best all-round operating system on the market. Good for beginners and serious programmers alike.
When Linux users ask me what the hell they're paying the extra money for when it comes to Apple, i just say:
Immaculate design.
Which they brush off as superfluous. They are mistaken. Design is everything.