It would be great to have separate search histories for subject field and for poster field. They clearly have no business being together. It is difficult to find posters among subject searches, and worse - they get pushed out because the drop box with the search history has a limited number of entries. With a separate search history for posters, I would likely have all the posters I need right here in the dropbox at all times.
And it is more difficult to remember and to enter posters again each time they are pushed out by completely unrelated subject searches.