I've been trying to figure out how to have iTunes store different content like movies onto an external drive but keep the rest of it local. I've just move my AddressBook archive to drop box using a symlink, anyone tried it with iTunes content?

Works a treat

iTunes won't write to it, need to rethink

You can move the whole iTunes library, that’s pretty straightforward.

You can also store some content outside it, provided that content wasn’t bought in the store or ripped directly into iTunes. For instance, movies ripped from DVD or MP3s from Amazon, emusic etc. can be stored anywhere. In Preferences»Advanced uncheck “Copy files to iTunes Media folder when adding to library”.

To do this with existing content, delete it from the iTunes library and choose the “Keep File” option. Then move the files to a new location and add them back to the iTunes library, once the ““Copy files…” option is unchecked.

If you’re bothered about lost metadata — play counts, for example — then there are scripts to restore that: http://dougscripts.com/

And here’s a simple Service for adding files to iTunes: