IAD is a nightmare on just about any day after 3:00 PM in my experiece. If it's a weekend from Friday to Sunday then it's twice as bad. Chalk this up to the international departures for Europe that are scheduled by just about every single airline flying out of IAD. I try my best to avoid scheduling departures out of IAD in the late afternoon for domestic flights.

Customs at IAD is no worse than MIA where I don't even feel like I am arriving in the US.