This is quite obscure and not a big deal, but I thought I’d mentioned it. Basically, undo doesn’t work right in one niche situation.
- Hook two items together
 - Unhook one item (Cmd+Backspace)
 - Open a new, third item in Hookmarks
 - Press Undo (Cmd+Z)
 - It will rehook the previously unhooked item to the new item, not the item it was originally hooked to
 
It should either re-hook to the original item it was linked to, or failing that, just do nothing. Linking to the new item doesn’t make sense as an undo option.