My wife and I have had a "business" FedEx account for over two years now. The advantages for us were FedEx Ground shipments to Canada and CODs.
However, there were also some problems too. On four occasions, when my wife dropped off packages at the FedEx office, we were charged for pickup. Something like $11 extra. They immediately charged our CC. On each occasion, there was a four to six month lag actually having our CC recredited for the amount they overcharged.
So now, we just pay cash up front instead of using the account.