If you have a new iPhone, iPad or Apple appliance, your gamma, which is how grays are shown, is probably set to 2.2. Snow Leopard changes your gamma from 1.8 to 2.2 without asking you.
Apple used to ship Macbooks with the gamma set to 1.8, but recently cranked up the contrast so things will look snappier on the shiny, glare-prone screens.
The images on this blog are scanned or adjusted to look right on a display set to a gamma of 1.8. I use a shiny screened (annoyingly glare-inducing) Macbook Pro, which is great except for the gloss, and I have set it to 1.8.
You will miss much of the tonality of the New55 photographs unless you lower your gamma. You can change it by going to display properties and working your way through the menus.