Just did a music test and I personally can’t hear much difference betwen two music files I tried. One was a 320kb VBR/44.1kHz file, the other a 192kb VBR / 48kHz file of the same song (She’s a Rainbow by the Rolling Stones). For some reason that song was so easy to hear it being slow on my Clip with the previous firmware when sampled at 44.1kHz; Jagger’s vocals sounded sluggish, the piano slow, and Charlie Watts’ drums were draggy sounding. With the latest firmware it’s gone. The 48kHz and 44.1kHz files sound pretty much the same.
I found that approxmiately 5 cents is the threshold of when humans can (usually) detect a pitch error. Musicians are likely more sensitive to pitch, so 5 cents may not still be good enough for them. This web page explains it better than I can:
The Use of Cents for Expressing Musical Intervals
My Clip is right at ~5 cents fast, previously it was 21 cents slow. That’s a huge improvement and now is at or below the threshold of my hearing. Not iPod accurate and not as accurate as my comparable Creative Zen Nano 1GB but lots lots better. I’ll take it and run. 
One annoying quirk I did find with the new firmware was sporadic switching from MSC mode to “Auto” after ejecting the Clip from the PC’s USB port. I never had it happen before but it’s done it to me twice now but I can’t reproduce this consistently. I noticed the couple of times it happened after I just unplugged it from the USB slot, didn’t eject it from the systray (I’m using Windows XP). Not a big deal, just don’t flip out if after updating your Clip it sporadically switches to Auto mode instead of MSC mode.
