I stumbled upon this really cool web site experiment.
The author takes the audible information that is lost when converting to MP3 and makes it a separate track. It is truly eerie and also an interesting thesis.
His prime example is Suzanne Vega's Tom's Diner which was apparently a benchmark song in developing the MP3 compression format.
Check it out!
http://ryanmaguiremusic.com/theghostinthemp3.html
Personally, at 320kbps and up I am satisfied with the sound in most cases. That said, I have been slowly converting all my CDs to FLAC and much prefer it; especially as it seems to gain broader acceptance as a viable sound format amongst manufacturers of playback devices.
Cheers,
Warren