I use filters quite a lot for examining & cross-checking my tag data. I find I have a number of filters set up which are almost identical, save for the target value (e.g. Rating = 2stars, Rating = 3stars, Rating = 4 stars).
I keep hoping for a dummy value to put into the filter definition, which would pop open a dialog box when the filter is applied, so that I could enter the specific value I'm looking for. (e.g. Rating = ? and I supply 2, 3 or 4 as required).
The Rolls-Royce version would provide a drop-down list in the dialog prompt which is based on the data already in the database, so that the value for the filter could simply be selected. It would probably need to allow for a value to be entered as well, so that a filter such as Title starts with ? could be used to find all titles beginning with "Blue", rather than looking specifically for "Blue Moon" or "Blues In The Night".
I appreciate that this might be tricky to implement for more sophisticated filters, but if it was possible only for one field in a filter, it would simplify my filter maintenance quite significantly.