At the moment I'm focused on -- and loving, the virtual date hierarchy.
This does sound great though:
What I will probably try to add soon, is a feature that will be a little smarter about rescanning -- so that if you have a giant folder you are working with, AND you let it do an initial completed scan of that folder, it will thereafter (on the same run) not have to rescan as you pop in and out of subdirectories.
-mouser
As said I'm loving virtual date hierarchy -- finding amazing screenhots of images (older photos mostly) that I made years ago.
Also, for what this is doing, it's really fast

I currently have the virtual hierarchy in a narrow column on the left; I increase the size of the thumbnail pane to most of the screen, leaving a small token column on the right for the actual preview/viewer pane.
Reproducible bug:
Using that slider I reduce the size of the thumbnails to below 30. The thumbnails go from showing maybe 25 thumbnails to showing just one image in the pane.
FWIW using keyboard to navigate gets confusing:
when focus is in thumbnail pane, focused file is highlighted blue -- this remains the same when focus is moved elsewhere (via tab key) which makes it difficult to know where one is when nothing else is highlighted. I can see when focus is in the hierarchy -- virtual or real, also when in one of the filter fields and the root but then I lose it and find I have to use the mouse to get back to the thumbnail field.
In fact I dont think I can tab to the thumbnail pane at all(?)