I use a USB dongle because my laptop, like most in recent years, doesn't have a serial port. The information above works great, and Ubuntu (Hardy) picked up the dongle immediately (Belkin brand dongle):

[ 5194.788330] usb 3-4: MCT U232 converter now attached to ttyUSB0

So /dev/ttyUSB0 is the device I used. Don't forget for Cisco/Juniper/Foundry to turn off hardware flow control and switch the speed to 8-N-1 (I'm spelling this out for googlers). This actually works much better under Ubuntu than it did in XP with vendor-supplied drivers, where it would bluescreen my box, hardlock it, or simply do nothing.