I confess that I only use this feature once in a while. But there is an aspect that seems odd when I do.
When I have a Virtual Library selected, if I add a new book that doesn't meet the VL's criteria, it shows up in the library list until I do a search. Same thing with changing an existing book so it no longer meets the VL criteria--it still appears until I do a search.
I assume this is an artifact of the way it's implemented with the search mechanism. But I can see it confusing a user who doesn't realize that.
I'm also puzzled by <None> appearing on my 'Additional Restrictions' list twice. Presumably once for itself and once from remembered searches?