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The Apple support document How to use multiple iPods with one computer suggests a number of ways for managing the media content on multiple devices. I use the Sync with selected playlists method with a slight twist. Rather than regular playlists I set the grouping field to indicate which users should receive which tracks and create smart playlists based on the content of this field.
e.g.
"Alice's Tracks" is "Grouping contains Alice" + "Kind contains audio"
"Bob's Videos" is "Grouping contains Bob" + "Kind does not contain audio"
Tracks that both Alice & Bob want on their iPods have the grouping set to "Alice/Bob"
etc.
I currently manage our family's five iDevices using this system, each getting a different selection to suit their tastes and the capacity of their device. An advantage of using the grouping field is that it is stored in file tags (for non-wav audio files anyway) so that it is relatively easy to recreate the playlists should the iTunes library get trashed and need rebuilding. Also useful if you move files about manually as playlist membership is preserved when you delete & re-import the tracks.
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