with ACDSee, at least, you can assign rankings, labels or notes to individual files or groups of files that are then stored inside the ACDSee database.
so, as an example, you could have several different folders that contain a variety of different images but you have assigned a label of 'hats' to some of the images inside each of these folders.
by clicking on the correct button you can then view all the thumbnails that have been labelled as 'hats' as a collection inside the normal thumbnail viewining panel as if they were all inside a single folder.
also, ACDSee allows you to click more than one folder to view in the directory tree - the contents of each folder are then collected together in the thumbnail viewing panel, just like they were all part of one folder.
the combination of being able to select several folders, labels, rankings and notes all at the same time is an extremely powerful feature - of course, this all depends on how methodical you are at categorising things in the first place.
(i don't feel up to doing a full review but i'll offer opinions on ALL the programs that end up being in the list - if it helps.)