ssh host touch 'hi there'           # fails

It creates 2 files, hi and there. Instead, do this:

    cmd=`shell-quote touch 'hi there'`
    ssh host "$cmd"

This gives you just 1 file, hi there.

    eval set -- `find -type f -print0 | xargs -0 shell-quote --`

    debug() {
        [ -z "$debug" ] || shell-quote "debug:" "$@"
    }

With echo you can't tell the difference between "debug 'foo bar'" and "debug foo bar", but with shell-quote you can.

    user_switches=
    while [ $# != 0 ]
    do
        case x$1 in
            x--pass-through)
                [ $# -gt 1 ] || die "need an argument for $1"
                user_switches="$user_switches "`shell-quote -- "$2"`
                shift;;
            # process other switches
        esac
        shift
    done
    # later
    eval "shell-quote some-command $user_switches my args"