United Airlines delay and rescheduling resulting in long waits, bad seat assignments, last minute notification Nationwide

You first need to know the reason for the delay.  If it was for weather or air traffic control reasons you are out of luck.  If it was for mechanical reasons that is a different issue.  Unfortunately, when you purchase an airline ticket these days you are subject to the their Contract of Carriage (COC).  This contract permits the airlines to operate with many legal protections all in their favor of course.  Essentially, the only obligation an airline has is to get you from point A to point B.  It doesn't matter how long it takes or what seat you fly in. 

This especially true when delays and re-routing are due to weather.  The only remedy you have is instances of IDB (Involuntary denied boarding).  This occurs when you are bumped from a flight for non-weather related issues, such as overbooking.  Then the airline has to pay cash compensation based on how long it took to get you to your final destination and if stuck overnight then it has to pay for your meals and lodging.  However, in your case if the delay was due to weather (I am assuming that it was) then there is not much that can be done.