In an article by MaximumPC, they had four music listeners described as "The Hipster", "The Curmudgeon", "The Audiophile", and "The Pluralist" suppy a track of their own that they knew inside and out on a CD. MaximumPC then proceeded to rip each track via iTunes three times, at different bitrates. Uncompressed WAV, 320 Kb/s(VBR), and 160 Kb/s(VBR), to see who could tell the difference. The music listeners could repeat sections, turn up the volume, analyze the mp3s any way they wanted.
To see what the results were, and the full article, you can read it here:
What do you guys think about bitrates? I've got Shure E3C earphones and anything encoded at 128 Kb/s I can hear a distinct hiss in the background. I prefer around 320 Kb/s