Done. I mp3gain'd the entire library (approx 100gb) using album gain at 93db, which took about 24 hours. I had 11 errors out of about 15,000 songs, mostly file naming issues which I quickly fixed and re-mp3gained. I then restored (including 'upgrading' to 1.2.3 firmware) and reloaded the pod. The reload (I only sync about 65gb to the iPod) went
much faster than it has before, about 2 1/2 hours instead of 5. Not sure if that is attributable to 1.2.3 or the fact that I turned off my real-time virus scanning, or something else or a combination of factors. Pretty sure it doesn't have anything to do with mp3gain
I am cycling at random through my '5 star' playlist as I speak, so skipping from one album to another. The tracks are
extremely well normalized. Although mp3gain said probably 30-40% of the songs showed clipping, I can't really hear it, and the increase in headroom (max volume) on the iPod is fantastic, just what I wanted. No annoying bump in volume at the end of non-faded songs either. The tags and album art in iTunes seem fine. This is with a mostly guitar rock, alternative, and electronica playlist, and I don't claim so have the best hearing (although I have great earbuds), so YMMV but I so far I am impressed and wish I'd done this long ago.
I also experimented with changing the gain on a few albums, just for fun. Changing the gain value once the album has been scanned is practically instantaneous. Very cool.