No-one has been able to prove they can tell a difference between a CD and 320kbps MP3s in proper blind tests though, including top professional sound engineers etc.
There's been various other threads where I posted links. Out and about on my phone at the mo so I CBA finding them right now. Not meaning to derail your thread but I've worked as a sound engineer and have a degree in music/music production and I've looked into this quite a bit and I'm confident it's true.
On this I absolutely agree with Grum. I found an app that could play FLAC files, plus I converted some FLAC downloads to lossless, and put those on my phone, just to do a comparison with my usual 320Kb ripped files. Listening through UE TripleFi 10 Studio monitors, I really couldn't hear any significant difference in sound quality, certainly nothing that made it worth the loss of space that having lots of music in those formats would entail.
I remember the Gadget Show once did a blind comparison using some seriously high-end audio kit, playing the same tracks on vinyl, CD, and 320Kb AAC, and the unanimous verdict was that the 320Kb tracks on the iPod sounded best!
What I do know is that there's a far greater difference in track quality depending on how the songs were originally mastered than there is between FLAC/Lossless/320Kb AAC(MP4).