I'm certainly no apologist for the new Continental in United colors (and even that's only half true), but I do know more than a little bit about scheduling and ground operations. It most certainly is possible to turn most aircraft around in well under an hour. What takes the longest time is baggage handling and, in some cases (especially Airbus 320 family), fueling.

Not sure what the exact problem was in your case, but it sounds like an aircraft is being rerouted for maintenance purposes. Generally, in long-term schedule planning the aircraft will be routed so that they cover every possible flight for the given type before starting the cycle over (note: this is for US-based airlines, not European airlines with separate fleets operating from each hub). As we all know, though, weather and other issues conspire to destroy that plan before it goes into operation.

Each individual aircraft has to be routed so it is in a maintenance city every so often for different types of maintenance checks. Logically enough, the airline wants to get the most flying legally possible out of an aircraft, which results in these reroutes. A reasonable scenario for your case is that the inbound aircraft would normally do, say, an LAX-EWR-LAX turn after arrival (I'm not looking at the schedules, so this is hypothetical), but now doesn't have enough hours remaining to do so and is instead doing an LAX-ORD-SFO turn.

That's a simple explanation that may be and probably is not applicable to the situation you experienced. The point is just to show that the basic scheduling is probably within reason.

BTW, I've seen a 757 turned in 32 minutes at ORD, when a diligent effort was made. I think it's the diligent effort that's mostly missing now.