regards the "!$may_cache" not above: What they were trying to say is things like "drupal_add_css" that used to be in that section should now be moved to "hook_init." AFAICT there is no equivalent section for real menu entries, but it is possible to use "hook_menu_alter" or "hook_menu_link_alter." I have not used either of those hooks yet. In the one case where I needed to alter the menu, I just included a line to clear the menu cache.
Also, now that a patch is available, I don't think this should be "critical" any more.
I just browsed your code. Anyone who looks at this patch might just get a better feeling about what it takes to make a major Drupal upgrade happen. Thanks for doing this.
I would like to see some "description" elements added to the schema, but this is really minor. And I don't think "disp-width" does anything; I really don't know what it is for. I've left it out of most of the modules I've converted.