I like MP3 format and using USB drives and such but take a MP3 and play the same CD song back to back. On a quality system you will be amazed how much difference there is. Its the little things that make the music come alive.
Like Seals "Loves Divine" you can hear the background noise level difference when he goes from one sample to the next on CD but its almost gone on the MP3.
Or Yes Talk where you can hear him take a breath before the solo and its not there on the MP3.
Or Fleetwood Macs "You Make Lovin Fun" where the cymbols just sizzel when Mick smacks them. They are only just a boring cymbol in the MP3 version.
Building a Better Spaceships "Bulletproof" where he goes into the quick drum transition. On CD when he smacks the drums they are alive and you can feel the kick. Record that CD to an iPod and all the impact of that transition is lost. You can hear it but no longer feel it.
I hate data compression.