There have been numerous blind tests between CD's, Lossless, and AAC's and MP3's at various bit rates. Do a Google search for that and see the many results. In very general terms, I've heard that about half the people can distinguish a difference.
Here's one study, an A/B comparison:
BLIND TEST: Lossless vs. MP3 320
A is Lossless 26% (38)
B is Lossless 42% (61)
No Difference 30% (44)
And the results of another:
http://www.music.mcgill.ca/~hockman/documents/Pras_presentation2009.pdf
Conclusion
- Trained listeners can hear differences between
CD quality and mp3 compression (96-192 kb/s)
and prefer CD quality.
- Trained listeners can not discriminate between
CD quality and mp3 compression (256-320 kb/s)
while expert listeners could.
- Ability to discriminate depends on listeners’
expertise and musical genre
- Artifacts can be verbalized and do not depend
on musical genre
I did an A/B comparison on myself. I can plug my phone into my home stereo. I had previously ripped a CD into 256K AAC. I compared a track on my phone to a track on the CD. It took a moment to do the switch, and after several switches, I concluded that I could barely tell the difference. I had to listen to specific things, like a cymbal or particular lyric to distinguish it.