Personal experience: most people can not differentiate anything above 128kbps mp3. Some can, but don't care. A lot of people listen to music in noisy environments with lower quality blue-tooth devices that decrease audio quality even more and make it way harder to differentiate from anything better than 128kbps mp3. Most current music is heavily dynamic compressed leaving very little space to differentiate better codecs. And the new generation of listeners is getting so used to compression artifacts that a cleaner sound may feel strange and unfamiliar.
The German c't magazin did an extensive test back in 2000 using pricey audiophille equipment (Sennheiser Orpheus, B&W Nautilus 803). 256k MP3 was statistically tied with the Compact Disc source.
