oklAAhoma

I've experienced several 3-4 hour delays, although by no means have they occurred regularly, more like once every few years or so. (Knock on wood.)

The most memorable:
DFW-SEA. I was PLT at the time and had chosen not to upgrade (for some idiotic reason). Summer storms at DFW were causing delays. We sat on the tarmac for 4+ hours waiting for our turn to take off after the 50 or so other planes that were ahead of us in the queue.

DFW-COS. Again I hadn't upgraded. IIRC it was one of the last years I was still PLT and it helped convince me to shoot for EXP. Again storms at DFW slowed everything down and we waited 3.5+ hours to take off.

DFW-ORD-BRU. We were delayed leaving DFW for 3+ hours because the wind at ORD was causing problems. According to the pilot only half the runways at ORD were available for landing, so flights were being held at the departure airports. I had scheduled a long connection at ORD, but we ended up just missing the flight to BRU anyway.

?-DFW. (I had been in Austria but I absolutely cannot remember the route I took to get home.) At any rate, we were diverted to IAH due to weather problems at DFW. We weren't allowed off the plane for 3+ hours after landing as the pilot hoped to head to DFW when the weather cleared. Finally, sometime after 10pm, the decision was made to cancel the flight for the evening and try again the next morning. I had already had more than I could take, so I rented a car one way and drove to DFW. (The amusing thing was at the rental return I ran into a guy from Texas who had been diverted to OKC. We joked about our bad luck as he would have much prefered a diversion to IAH, and OKC would have been more convenient for me.)