I'm very grateful for this thread. I installed it on my iModded 60gb photo iPod and from what I can tell the improvement in sound is well worth the hassle. I say 'from what I can tell' cos so far I've only heard it playing thru my computer speakers. They're pretty good for computer speakers, being Monsoon (kinda mini-maggies), though not up to the quality of my main rig.
If it sounds this good on 'puter speakers oughta be aweseome on my main rig.
I'm also a Mac user; but I've got one of those new MacIntels with a dual boot into WinXP natively, via Apples bootcamp, which is beta software. That's one point to note folks: Rockbox isn't even at the beta stage yet, so use at your own risk. i don't think the risk is so high though, since installation is completely reversible back to Apples standard iPod firmware.
You really do need access to a Windows machine to make this as hassle free as possible and if you've previously used your iPod under Mac you have to not mind losing all the current music and data that's on it, since you'll need to re-format the iPod for FAT32 and that means running 'Restore' from ipodUpdater under windows.
After that, just follow the instructions on the Rockbox wiki or the pdf. Just a few command line entries basically and a reboot of the iPod and off you go.
One gripe I have is the way it relates playlists to folders. It got me quite confused and I need to play with it some more before I hook it up to my main rig.
For me it is worth it though for the sound quality and the ability to play flac, since I already have a lot of ripped CD's on my HD in flac format.
Hope it helps!
geoff