I had that requirement as well. Solved it with xplorer²
which lets you see the files in a folder and in all its
subfolders as a virtual single flat file - i.e., as though they were in a single logical folder. Very
useful for mass file operations.
Not a good idea to actually keep the files in a single logical folder though. Keeping the files in date-related folders helps for ease of reference and cataloguing and eliminates the problem of too many files (e.g., thousands) in a single folder - which latter tends to slow Explorer down when browsing a folder and then file management becomes very laggy.
For image-viewing and cataloguing/tagging, then consider Picasa
, which doesn't seem to mind large numbers of files in a folder. Refer Google Picasa "Sunset" version - Mini-Review and anchor-point