Currently it is possible to search for a user based on:
When logging a call. A number of customers use login ID as a way of identifying users but to find them they need to also populate attribute 1, which then cannot be relabelled in the search/default search options.
This did not make v9.9 and is in the Product Backlog for inclusion in a future release.
QD Fields in Core are planned to be the same as QD fields in the Self Service Portal in that you can configure which fields to search on and which columns to display. This is planned for v9.9 but as with all features the scheduled release is subject to change.