The other thing to know is that if you symlink something into the Dropbox tree, Dropbox will happily sync it properly. I'm using this feature to keep my music where iTunes wants it, but with a symlink from ~/Music/iTunes/iTunes Media/Music (or whatever) to ~/Dropbox/Music.

Dropbox treats that symlink as though it were a real directory so far as the other client machines go, so anywhere I don't explicitly exclude ~/Dropbox/Music from sync, it'll just pull all the music across as a directory rather than as a symlink.

This may be useful if for some reason you really want stuff in random directories in different places but still want Dropbox to sync it all.