Annoying special cases:

    $ cd /
    $ nm=/foo
    $ ls | grep nm
    $ cd nm
    $ pwd
    /foo
    $ cd ~
    $ ls | grep nm
    nm
    $ cd nm
    $ pwd
    ~/nm
    $ echo FFFFFUUUUUUUUU

Inflexible:

    $ cd nm/jan/img
    cd: No such director nm/jan/img
    $ echo SHIT
    SHIT
    $ cd $nm/jan/img

Worse, It's nonstandard and only saves you one chracter.