Worst design decisions?

The hands-down winner, so far, is the Cisco
CMS-formerly-known-as-Arrowpoint, which has an RJ45 console cable
which WILL NOT WORK, full stop, with the RJ45 connectors on Cisco's
own console servers.

*wild applause*

Ah, yes. I've run into that bad boy. It really stinks to come in to
work in the middle of the night to troubleshoot a problem and you know
there is only one serial adapter that works with the Arrowpoint CSS and
you can't find it! Once I found it I marked it with bright tape and
wrote a big A on it with a magic marker. I then made sure everyone in my
department knew what it was and where it was.

I personally feel that the biggest benefit to upgrading to the new CSS
was getting a 'normal' console connection.