For those who did not read the article:

Difference between using usual 22 and "unusual" 24 port, 18000 attempts vs. 5 attempts over one weekend.

Seems to weed out script kiddies quite quickly.

Personally, I don't see anything wrong with having 3 locks on the door:

  ACl
  port knocking
  nonstandard port

Another analogy would be one bouncer, one secret knock, and one nonstandard keyhole.

Of course, one still wants to have a difficult to pick key after all that.