I do (rarely) notice a difference between FLAC and 320 or VBR V0 mp3, especially in high frequencies.
Try this: open a FLAC file with Audacity and then click the track name and click on Spectrogram.
Now convert the same file to mp3 @ 320kpbs and do the same with audacity.
There must be an imaginary line in the mp3 file in >14Khz frequencies, that's like a "threshold" where the lossy formats can't exceed.
But hey, 99.9% of music is in the 30Hz-12KHz frequency range, so there's nothing to worry about.
Cymbals, violin, snare and solo guitars are the instruments where you might notice a different.
Of course there's more compression than a simple threshold, you will notice that the mp3 graph is less colored and with less peaks, but that's hard to interpret for a normal human.
This example works better with rich dynamic range songs, modern music is wrong in so many ways.
(You can view the difference in Analyze -> View Spectrum on audacity's menu too.)
Off Topic: I think the lossless formats like FLAC/ALAC/APE were not made for listening purposes but for storage, and WAV was made for music production in the digital era.