Thanks for the tips
Just noticed this: if the current list includes books that are marked, then the list row number space will be wider even if the marked books are not visible. Perhaps the top left corner cell could be decorated with marked.png if there are any marked books in the current list.
And, thanks for the upcoming Manage Cats tool, pity about the Apply Cats option. Bloody things never do what's expected of them… cats that is
BR