Version:           1.0.0 (using KDE 4.3.4)
OS:                Linux
Installed from:    Fedora RPMs

Given that a picture is taken by a specific camera at a specific time, if you associate metadata with a camera at a particular time, then any picture taken at that time can be automatically given metadata.

For example, if I take a camera on a trip and I'm in London from date 1 May - 5 May and Paris 5 May - 10 May, then a picture taken on the 4th can automatically be tagged as being in London, and 7th, Paris.  (This is a generalization of correlating GPS data to a picture timestamp.)

This can also be used for events ("Fred's Wedding" was on date 11 June), camera settings ("Used a old Nikon prime for this shoot on this date"), etc.

This requires that on import, an image can be associated with a particular camera.  Once that association is made the image metadata inherits the camera history metadata.  The camera metadata may be set up after image import, so it isn't sufficient to just assign the metadata at import time.

This allows a lot of useful boring metadata to be set automatically, and is a more general extension of using the implicit EXIF data and/or GPS traces (which may not be available).