IAD is the only airport I've been to where I've spent an hour at immigration and then walked through to the luggage claims hall to find that my airline's ground handler still hadn't loaded bags from my flight on the carousel (note this was a full hour at least after arrival) so I had to wait even longer there! Every other port I've had long immigration processing, the good thing was my bags were usually already on the carousel. Interestingly, LAX on the other hand was a breeze, my bags was already on the carousel just as I walked in the hall. A brisk walk to intercept my bag as it rolled around and I was outside within minuites. YMMV but IAD is not an airport I'm keen to use anytime soon! :)
Immigration at Dulles is faster than it used to be, at least for Americans. They're expanding the automated system, with a lot of kiosks. (I'm not entirely sure how that's different from GlobalEntry.)
Which just gives you more time to wait for your bags, I'm afraid. They're building a lot of new infrastructure which might help eventually.
