+1 for seeing the WithinDateRange filter and field working.
..further to Enclave's suggestion I can imagine the SearchFilter form system allowing you to choose either:
search value,
search between,
search greater than,
search less than
ie allowing the user to customize how the search is done on the form, and the form will modify itself appropriately, such as showing two input boxes for searching between values.
..this should be made into a trac ticket, or discussed on the ss google dev group to actually see / hear about any progress.