Once you’ve done a Finder search and saved it as a smart folder, opening the smart folder (usually from the Saved Searches section of a window’s sidebar) displays only the “hit list,” and not the criteria you defined for the search. There’s no obvious way to edit the criteria, but all you have to do is select Show Search Criteria from the window’s Action menu (the gear) to display the criteria bars from the saved search.
Edits to a smart folder’s criteria automatically become part of it, without your having to explicitly save the changes.
Note: This item contains 2 implicit interface criticisms: the un-obvious way you get to the original criteria (who looks in that Action menu?) and the name – and icon – for that ubiquitous menu: the official name is “Action” but so few people know that, and the gear icon used for it is so lame, that I’m incredibly tired of having to type a parenthetical (the gear) every time I refer to it!