I use this airport mainly to connect from United's Int'l flights to its domestic flights. Although connecting passengers are to use separate Immigration and Customs at C concourse the situation is even worse in comparison with Chicago-O'Hare or Los Angeles where you have to move from one terminal to another. In my past two trips this year both of which involved Int'l to Dom transfer on UA there were 90 mins between arrival and departure. This was much longer than the minimum connection time published by United. On both occasions I did not have enough time (my first occasion I made the connecting flight 5 minutes prior to its departure time and the second time I was able to make a connection because the outgoing flight was delayed for 2 hours). There are too few immigration officers to handle passengers during the peak time (around 3-5pm) in which a number of 777s and 747s arrive almost every 5 minutes. What made it even worse was the train to connect terminals. If you were connecting to flights (esp. UA Express or Continental) leaving from A concourse you have to walk to the middle of C concourse go down the stairs backward wait for a train then once you have reached the concourses A/B you have to go all the way up to cross a bridge to go to the gate areas. This would normally take at least 25-30 mins compared to the time when there was a mobile lounge operating between C and A. The airlines seriously need to consider revising MCT at IAD.