The difference I can hear is in the dynamics of the sound. With a CD the frequencies from 1k to 8k sound flat. Almost every time I have tested this theory I can hear a warbling a bit and a slight rise in those freq in that frequency range. I do not know why this is but I do very critical listening for a living and have tested this out in a few different studios with the same outcome. I am sure the low end is affected as well but I myself couldn't tell if the was a change. Although the difference is slight it is definatly there....
Well I sure can't. For me it's...
192 to 320mp3 -> Can tell the difference, especially in bass extension and treble chrispness.
320 to CD or lossless -> Can't tell the difference if a friend swaps them randomly.
CD or lossless to vinyl -> Generally can tell an improvement depending on the recording, most of my vinyl recordings are significantly better than the CD counterpart, often because the vinyl has more dynamics because if its pressed too loud/live the needles won't sit. Bass, especially my genre of music, generally is better on vinyl.
SACD still sounds the best to me for acoustic music, for electronic music I don't notice an improvement over vinyl.
DVD-A to SACD - Can tell they are different, but can't tell you which is which.