I use Bank of America's online banking billpayer service because it's free. I got nailed with a $29 late fee on my Visa last month even though BofA showed that my payment was made three days prior to the due date. I called my bank to complain and found out that they actually mail out a physical check to pay my bills so I should allow five days for payments to reach the providers.
This strikes me as incredibly silly, like finding out that the great Wizard of Oz is just a little man behind the curtain, or like finding out that Wolfgang von Kempelen's chess-playing automaton The Turk was operated by a dude hiding inside the machine.