I have found that the USB world has not really taken over ham radio yet, sure there are some USB devices out there but not many. If you are like me you have more serial cables that you do ports on your computer. Most if not all new laptops only have USB ports. As for PC's they may come with a total of one. There are the USB to serial converters but I find them to be a bit fussy at times to set up and get good communication going. Last year I came across a product called Edgeport
from Digi international these units can take up to 16 serial cables and with only one USB cable going to the PC. I have the 4 port model and found it on Ebay for about 60.00. Over the past year I have found this unit to work great. You can have all serial cables communicating at the same time. I have never noticed and troubles or slow downs. This is a great solution for the shack with multi serial cables and not enough ports on the PC. If you need it for portable use such as field day it's great as it gets it's power from the USB port so no external power source is needed.