The contacts get dirty, they dont fit some USB ports properly, they die regularly, are absolutely no good if you don't have a USB port handy (my desktop for example doesn't have a USB hole in the front or on the keyboard or monitor, resulting in crawling around under my desk to authenticate) and to be honest quite fragile.
I've got some hard to access USB ports, too. I solved that problem by buying some USB extension cables (male on one end, female on the other). They are very inexpensive. Give them a try, you won't be disappointed. No more uncomfortable hunting for USB ports under the desk!