Alot of network equipment, like routers, firewalls and switches, still often have serial ports to allow configuration, if the normal network connection is somehow unreachable.
Serial console box Edit
Serial ports aren't exactly in abundance these days, so it might be good to find an old laptop and keep it just for the odd moments where you need this. For this purpose you can use any old 386 or better and it needs only 4MB RAM. It doesn't need to be one of those 386's with a math co-processor.
You can write PiTuX to a floppy or CD. Boot the media on the old laptop and voila. It automatically starts a terminal program (minicom) and you can just plug a serial cable between the computer and the network device and then you're connected to it.