Yeah, the B concourse is actually pretty nice. Good plane watching, and much wider, lighter, and airier than C or D. I do a lot of transiting through IAD, and many of my UX flights go through concourse A, which really is a dump. One bummer not mentioned here is that there's no RCC in concourse A, so you have to allow time to ride the moon buggy from C or D. Not that it matters, since the RCC's at IAD are always packed to the gills anyway. The only redeeming feature in all this mess is Five Guys.