That's an interesting technique that I've never heard of. Do you have fast shortcuts/keybindings for removing the # when you are ready, or is it '(left arrow x N) + ^H' each time?

In windows what I do is Home->Delete I am amazed at how useful home, end pgup and pgdown keys are, and I am pretty sure not many people know or use them a lot.

^A ^D

^A ^D it is. But since you bring up moving the cursor, it also is very helpful to 'xset r rate 160 80' to speed it up substantially in Xwindows.

I assume (by trying on zsh) that this is a configuration change you made vs. some keybinding I've yet to discover?

Those are Emacs style keybindings, which are the default on most shells. You've probably switched to Vi style bindings in zsh.

Readline bindings, emacs mode.

Despite (mostly) using vim as an editor, it's got to be emacs on the shell itself.