In summer 2005 I flew Newark-Memphis with Continental (Expressjet?) on an EMB-145, and the flight was delayed for several hours due to a massive storm right on the airfield.
Unfortunately for us we spent the time in the aircraft awaiting a slot and pushback, rather than sitting at the terminal - the crew were keen to get a slot and be on their way, and didn't expect to have towait so long, and the start time kept getting pushed further and further back
Think in the end I spend just under 8 hours on the aircraft, most of it at the gate in Newark - thankfully I had the front row seat by the 'galley' which affords slightly more legroom than most, but it was still damned uncomfortable since I can't even stand in the aisles as the ceiling is too low in this type of aircraft. Think the flight crew were almost out of hours by our arrival in Memphis - had the delay been much longer they'd have had to be relieved by another crew before departure.