It would be nice if Koha had a permission to limit access to the merge records option (Merge selected button) on the addbooks.pl search results page and the virtualshelves/shelves.pl page (lists). This is especially important in a consortial catalog environment where many people have cataloging permissions, but most probably shouldn't have the ability to merge records.
I would echo this request - our regional cataloguing group would favour this to be restricted to a core group of cataloguers/system administrators.