[Mad_Big_Sausage]

In my root right now (note: * = ROCKbox folders or files)

.rockbox* - Rockbox system folder
A_Music - All my music.
   Artist
     Album
        00-Trackname.whtevr
B_Music - Music I've gotten off friends
   Folder structure same as A_Music.
Games* - Files and folders stored for use with rockbox games.
Misc* - Files and folders stored for use with rockbox games.
Picture - All my pictures.
   Cam - My digital camera pictures sized to 3xH300 screen for viewing on my player
       Date, Event or Place
          Pics.jpg
   Misc - Other pics (eg email jokes, pictures I'm working on and anything really)
       Different folders depending on use and type
   Stolen - Pics I've taken off friends
      Friend's name
          Date, Event or Place
             Pics.jpg
   Z_Cam - Digital camera pictures in original format and size for sharing
Play - All my playlists go here.
Record - Default iRiver recording folder
Recordings* - ROCKbox recording folder
Videos - Speaks for itself
Y_Music - Music I've taken off friends that I havn't gotten around to tagging/naming up to my high standards yet.
   Folders are all over the place.
X_Music - Music that isn't of perfect quality that I havn't/can't replace.
   Folder structure same as A_Music.
Z_Music - Music that doesn't fit into an album. ie single songs.
   Artist - Track.whtevr
Z_Storage - Folder I use for storing files on the HD.
   Grouped in folders by type or use and whatever is necessary.
dynamic.m3u*
H300.hex* (Unrockboxed 1.29K in case something goes horribly wrong)
rockbox.iriver*

That's my format. It's all personal choice though.

Ask yourself:
What do use most?
How do you listen to your music? By artist, album, genre?
How much music do you have? Divide music up into A-M, N-Z?
Which folders do you use most?
Do you care what order the folders appear in? (Most used near the top and bottom?)
Are you as anal as me about all this??

Hope it helps.