[Originally posted on another MB a couple days ago]
So I installed RockBox - for those not familiar this is a complete replacement OS for your MP3 players (there are versions for like 30 or so models).
It has it's own filesystem management, MP3 library system, no iTunes, you just COPY files over by mounting your device as a harddrive.
I installed like 10 themes which range from decent to amazing (I'll shoot some pics or something). I also installed 50 fonts and like 30 apps - full on games, Gameboy emulator, chess, etc.
My IPOD now plays FLAC files, in native format - just copy them over. I had a remastered copy of Johnny Smith - Guitar Genius, and it sounded amazing. RockBox currently supports 15 different audio CODECS. There's also like 20 "advanced" auto settings
FWIW, it also plays MPEG files vs. having to convert over to a QT4 format for video.
The install actually supports dual boot - you do a menu+select reset and flip the lock over and it boots back to the original OS. However, the original IPOD OS needs to go through the whole song management routine (copying into special directories, updating its database), so anything you just regular filecopy over won't show.
Pretty simple install - copy of the .rockbox folder to the root and run a ipodbootloader app which installs the additional boot info. The only thing you have to make sure is your IPOD is setup as a HD type device which may require iTunes to initially configure.
When it first loads it comes up in this super minimal *NIX like interface, but a decent theme fixes that right up.
You can customize the tag database too which is pretty slick - so if there's another way you want to classify your music/playlists, you can setup what you want.
I haven't explored everything yet but pretty cool, free, and easily reversible.
...and my followup after a couple of days of fooling around with it
I'm offically calling it pretty sick.
Drag -n- Drop copy/delete without any filename translation, you can keep your existing folder structures, organization. You can just browse files like a desktop OS.
Music database has several more features, lots of customized views, extended searching.
Support for FLAC, OGG, MP3 and several more.
Dozens of sound config options, simple, advanced EQ's (even things like definable volume increment).
Same for themes ("skins") - album art, extra song info, custom scroller plugins, fonts, icons.
Extensible OS so there are dozens of home grown games and apps (all part of the standard package).
Since it's an open source project, it's sort of always a work in process, so it might not be as solid as the regular OS. The IPOD 5G version seems pretty stable though.
Video support seems a little off - I haven't experimented enough with MPEG files. I'm not even 100% sure it support QT in RockBox mode.
Here's a couple of skins I'm using (just the skin library, figured it was better than taking a pic):