Edward Weston's prints have a luminosity and depth that just cannot be appreciated from reproductions. It's also important, I think, to see them in their original size--all small contact prints no larger than 8x10.
I occasionally contribute to online photo critiques, here and at usefilm.com, but I always feel like I'm looking at the images in a colored, hazy funhouse mirror. You just have no idea what they really look like as prints.
I am fortunate to live in close proximity to galleries, and I probably get to see more real prints by great and not so great photographers than many people, but I never feel I do it enough.