Two suggestions

[jonha4711]

1. Adding keyboard shortcuts to open folders defined in the Favourites pane.

2. An option to export/import (as CSV, say) a simple list of filenames and their category values, including hierarchy information. Having such a feature would allow additional goodies like mass manipulating the category values with a capable editor (ie one supporting regular expressions).
[EDIT]
I have tried to simulate something like this (exporting filenames and category values) by opening the XnViewMP database (it's a basic SQLite file after all) and reading the relevant fields. Turns out that metadata seem to be stored in an opaque blob. Rather disappointing and (IMHO) not the wisest design choice, perhaps. It would be great if a future DB version used a more readable/parseable format for at least some of the metadata (it could still be a blob, but in XML or JSON format).
[/EDIT]