Why the pictures appear differently on different platforms
Apple-brand monitors and some aftermarket monitors designed for the Mac tend to be brighter than PC monitors. Several years ago, when I used a Mac at home and a PC at work, our IS guy came by my office and said "man, why do you keep your monitor so bright?" To me it just looked normal, as I was used to my Macintosh monitor!
So, when prepping images for use on both PCs and Macs, you have to find a middle ground.
Deke McClelland, in the Photoshop 4 Bible, describes this problem fairly well:
"Apple monitors -- and many non-Apple brands developed for the Mac -- are calibrated to a gamma of 1.8. Meanwhile, most PC monitors are calibrated to 2.2, which is roughly equivalent to a standard television.
Higher gamma values translate to darker displays because they indicated degrees of compensation. That is, an image has to be lightened only to 1.8 on the Mac to look as light as an image corrected to 2.2 on the PC" (p. 753).
There. Now you know!