There was an interesting (and sometimes quite amusing) discussion about Info on the help-gnu-emacs mailing list. Apart from learning that there exist people who do not even want to use the amazing Info mode, I learned that there is a very little known Emacs command Info-edit. It used to be bound to e in Info, but has been deprecated some time ago and now the only way to invoke it seems to be by M-: (Info-edit). It puts the browsed Info buffer into an editing mode; after the edit, you can press C-c C-c and be asked about where to save the edited file.
I do not plan to actually use it, but it is interesting to know that there exists such a function, possibly inspired by the American habit of making notes on the books’ margins. During the discussion, I also learned that before texinfo, Info files were created and edited by hand. (In that time, the Info-edit function made more sense, since nowadays they will get rewritten by each install of a new Emacs version – that’s exactly why I don’t expect to use Info-edit.)
Of course, if you want to save the Info file in its usual place (this is /usr/local/share/info, you need root privileges. This is not a problem in contemporary Emacsen – you just prepend /sudo:: to the (absolute) path, and Tramp kicks in: asks for the password and sudo-saves the file (assuming you have permissions to run sudo, of course).
This is yet another example of Emacs having many hidden gems sprinkled throughout its codebase. It is really a pity that this function is not useful anymore (both because each reinstall would overwrite these changes and because the command is deprecated). I wonder whether it would be possible to modify Info-edit so that it would jump to the texinfo source instead. In my case (I have full Emacs sources in the local clone of the Git repo), that could allow me to e.g. instantly fix some mistake and send a patch to the developers!