If you want a tags like column in which order is preserved you can create a custom column in Preferences->Add your own columns (check the box that says 'Contains names'). IIRC, order is preserved for tags like columns containing names, just like it is for the authors column, you will have to use & instead of , as the separator, however.
@davidfor: Order information for all many-many columns is stored in the link table, the order in which the entries for a particular book appear in that table is significant.
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