[MarioImpemba]

A private audio forum I belong to did a double-blind 320kps vs Flac ABX and could not accurately distinguish differences.
 
I absolutely cannot discern an audible difference with the same source material encoded to v0 vs. Flac over speakers due to the listening environment and quality of gear.
 
Doubtful that would change given better gear, but will try again once my headphone set up arrives.

 

[Bostonears]

I have all my CDs ripped to FLAC (for use with my Squeezeboxes at home) and also converted to MP3 VBR -V0 LAME (primarily for use with my iPods, where storage space is a limited).
 
I have compared the two formats back and forth many times using my best home audio equipment with both speakers and headphones. I only hear a subtle difference between the formats on albums that are really well recorded and mastered. (When there's an audible difference at all, it's most noticeable in the sound of cymbals.) I estimate that the two formats are indistinguishable on more than 90% of my albums. Nevertheless, I intend to keep all my music as FLAC files for archival purposes. Even if new compressed file formats emerge in the coming years, I'll always be able to generate them from the lossless FLACs.