Hi,
(elisp)Key Binding Conventions contains the following text, discouraging
mode authors from binding C-h:
* Don't bind `C-h' following any prefix character (including `C-c').
If you don't bind `C-h', it is automatically available as a help
character for listing the subcommands of the prefix character.
I think it should similarly discourage authors from binding C-g, for the
similar reason that users might often begin a key sequence and then want
to stop before completing the sequence. Some users hit ESC in such a
situation, while others hit C-g.