I would like to propose a feature enhancement for gThumb.

In your help file, you highly recommend to use gThumb to rename/move folders or
images, since you will lose your comments otherwise. Unfortunately, catalogs
containing an affected image are not updated which results in false entries in
the catalog files. (And the image is lost from the catalogs point of view)

I think gThumb should try to keep the catalogs consistent on rename/move/delete
operations:
It should be possible to search through the catalog-files stored in
~/.gnome2/gthumb/collections and modify each entry, which is effected by the
users operation.
If you think, that this might not scale on large image collections, you might
think about adding some metadata (in the image folders) to each picture, which
contain the information, in which collection an images is part of...

Best regards,
 Matthias Schwarz